2.X.I. Miscellaneous.—2.X.II. Melastomaceae.—2.X.III. Correspondence with John Scott.
2.X.I. MISCELLANEOUS, 1843-1862.
(PLATE: SIR JOSEPH HOOKER, 1897. From a Photograph by W.J. Hawker Wimborne. Walker Cockerell, ph. sc.)
LETTER 575. TO WILLIAM JACKSON HOOKER. Down, March 12th {1843}.
...When you next write to your son, will you please remember me kindly to him and give him my best thanks for his note? I had the pleasure yesterday of reading a letter from him to Mr. Lyell of Kinnordy, full of the most interesting details and descriptions, and written (if I may be permitted to make such a criticism) in a particularly agreeable style. It leads me anxiously to hope, even more than I did before, that he will publish some separate natural history journal, and not allow (if it can be avoided) his materials to be merged in another work. I am very glad to hear you talk of inducing your son to publish an Antarctic Flora. I have long felt much curiosity for some discussion on the general character of the flora of Tierra del Fuego, that part of the globe farthest removed in latitude from us. How interesting will be a strict comparison between the plants of these regions and of Scotland and Shetland. I am sure I may speak on the part of Prof. Henslow that all my collection (which gives a fair representation of the Alpine flora of Tierra del Fuego and of Southern Patagonia) will be joyfully laid at his disposal.
LETTER 576. TO JOHN LINDLEY. Down, Saturday {April 8th, 1843}.
I take the liberty, at the suggestion of Dr. Royle, of forwarding to you a few seeds, which have been found under very singular circumstances. They have been sent to me by Mr. W. Kemp, of Galashiels, a (partially educated) man, of whose acuteness and accuracy of observation, from several communications on geological subjects, I have a VERY HIGH opinion. He found them in a layer under twenty-five feet thickness of white sand, which seems to have been deposited on the margins of an anciently existing lake. These seeds are not known to the provincial botanists of the district. He states that some of them germinated in eight days after being planted, and are now alive. Knowing the interest you took in some raspberry seeds, mentioned, I remember, in one of your works, I hope you will not think me troublesome in asking you to have these seeds carefully planted, and in begging you so far to oblige me as to take the trouble to inform me of the result. Dr. Daubeny has started for Spain, otherwise I would have sent him some. Mr. Kemp is anxious to publish an account of his discovery himself, so perhaps you will be so kind as to communicate the result to me, and not to any periodical. The chance, though appearing so impossible, of recovering a plant lost to any country if not to the world, appears to me so very interesting, that I hope you will think it worth while to have these seeds planted, and not returned to me.
LETTER 577. TO C. LYELL. {September, 1843.}
An interesting fact has lately, as it were, passed through my hands. A Mr. Kemp (almost a working man), who has written on "parallel r," and has corresponded with me (577/1. In a letter to Henslow, Darwin wrote: "If he {Mr. Kemp} had not shown himself a most careful and ingenious observer, I should have thought nothing of the case."), sent me in the spring some seeds, with an account of the spot where they were found, namely, in a layer at the bottom of a deep sand pit, near Melrose, above the level of the river, and which sand pit he thinks must have been accumulated in a lake, when the whole features of the valleys were different, ages ago; since which whole barriers of rock, it appears, must have been worn down. These seeds germinated freely, and I sent some to the Horticultural Society, and Lindley writes to me that they turn out to be a common Rumex and a species of Atriplex, which neither he nor Henslow (as I have since heard) have ever seen, and certainly not a British plant! Does this not look like a vivification of a fossil seed? It is not surprising, I think, that seeds should last ten or twenty thousand {years}, as they have lasted two or three {thousand years} in the Druidical mounds, and have germinated.
When not building, I have been working at my volume on the volcanic islands which we visited; it is almost ready for press...I hope you will read my volume, for, if you don't, I cannot think of anyone else who will! We have at last got our house and place tolerably comfortable, and I am well satisfied with our anchorage for life. What an autumn we have had: completely Chilian; here we have had not a drop of rain or a cloudy day for a month. I am positively tired of the fine weather, and long for the sight of mud almost as much as I did when in Peru.
(577/2. The vitality of seeds was a subject in which Darwin continued to take an interest. In July, 1855 ("Life and Letters," II., page 65), he wrote to Hooker: "A man told me the other day of, as I thought, a splendid instance—and splendid it was, for according to his evidence the seed came up alive out of the lower part of the London Clay! I disgusted him by telling him that palms ought to have come up."
In the "Gardeners' Chronicle," 1855, page 758, appeared a notice (half a column in length) by Darwin on the "Vitality of Seeds." The facts related refer to the "Sand-walk" at Down; the wood was planted in 1846 on a piece of pasture land laid down as grass in 1840. In 1855, on the soil being dug in several places, Charlock (Brassica sinapistrum) sprang up freely. The subject continued to interest him, and we find a note dated July 2nd, 1874, in which Darwin recorded that forty-six plants of Charlock sprang up in that year over a space (14 x 7 feet) which had been dug to a considerable depth. In the course of the article in the "Gardeners' Chronicle," Darwin remarks: "The power in seeds of retaining their vitality when buried in damp soil may well be an element in preserving the species, and therefore seeds may be specially endowed with this capacity; whereas the power of retaining vitality in a dry artificial condition must be an indirect, and in one sense accidental, quality in seeds of little or no use to the species."
The point of view expressed in the letter to Lyell above given is of interest in connection with the research of Horace Brown and F. Escombe (577/3. "Proc. Roy. Soc." Volume LXII., page 160.) on the remarkable power possessed by dry seeds of resistance to the temperature of liquid air. The point of the experiment is that life continues at a temperature "below that at which ordinary chemical reactions take place." A still more striking demonstration of the fact has been made by Thiselton-Dyer and Dewar who employed liquid hydrogen as a refrigerant. (577/4. Read before the British Association (Dover), 1899, and published in the "Comptes rendus," 1899, and in the "Proc. R. Soc." LXV., page 361, 1899.) The connection between these facts and the dormancy of buried seeds is only indirect; but inasmuch as the experiment proves the possibility of life surviving a period in which no ordinary chemical change occurs, it is clear that they help one to believe in greatly prolonged dormancy in conditions which tend to check metabolism. For a discussion of the bearing of their results on the life-problem, and for the literature of the subject, reference should be made to the paper by Brown and Escombe. See also C. de Candolle "On Latent Life in Seeds," "Brit. Assoc. Report," 1896, page 1023 and F. Escombe, "Science Progress," Volume I., N.S., page 585, 1897.)
LETTER 578. TO J.S. HENSLOW. Down, Saturday {November 5th, 1843}.
I sent that weariful Atriplex to Babington, as I said I would, and he tells me that he has reared a facsimile by sowing the seeds of A. angustifolia in rich soil. He says he knows the A. hastata, and that it is very different. Until your last note I had not heard that Mr. Kemp's seeds had produced two Polygonums. He informs me he saw each plant bring up the husk of the individual seed which he planted. I believe myself in his accuracy, but I have written to advise him not to publish, for as he collected only two kinds of seeds—and from them two Polygomuns, two species or varieties of Atriplex and a Rumex have come up, any one would say (as you suggested) that more probably all the seeds were in the soil, than that seeds, which must have been buried for tens of thousands of years, should retain their vitality. If the Atriplex had turned out new, the evidence would indeed have been good. I regret this result of poor Mr. Kemp's seeds, especially as I believed, from his statements and the appearance of the seeds, that they did germinate, and I further have no doubt that their antiquity must be immense. I am sorry also for the trouble you have had. I heard the other day through a circuitous course how you are astonishing all the clodhoppers in your whole part of the county: and {what is} far more wonderful, as it was remarked to me, that you had not, in doing this, aroused the envy of all the good surrounding sleeping parsons. What good you must do to the present and all succeeding generations. (578/1. For an account of Professor Henslow's management of his parish of Hitcham see "Memoir of the Rev. John Stevens Henslow, M.A." by the Rev. Leonard Jenyns: 8vo, London, 1862.)
LETTER 579. TO J.D. HOOKER. Down, November 14th {1855}.
You well know how credulous I am, and therefore you will not be surprised at my believing the Raspberry story (579/1. This probably refers to Lindley's story of the germination of raspberry seeds taken from a barrow 1600 years old.): a very similar case is on record in Germany—viz., seeds from a barrow; I have hardly zeal to translate it for the "Gardeners' Chronicle." (579/2. "Vitality of Seeds," "Gardeners' Chronicle," November 17th, 1855, page 758.) I do not go the whole hog—viz., that sixty and two thousand years are all the same, for I should imagine that some slight chemical change was always going on in a seed. Is this not so? The discussions have stirred me up to send my very small case of the charlock; but as it required some space to give all details, perhaps Lindley will not insert; and if he does, you, you worse than an unbelieving dog, will not, I know, believe. The reason I do not care to try Mr. Bentham's plan is that I think it would be very troublesome, and it would not, if I did not find seed, convince me myself that none were in the earth, for I have found in my salting experiments that the earth clings to the seeds, and the seeds are very difficult to find. Whether washing would do I know not; a gold-washer would succeed, I daresay.
LETTER 580. TO W.J. HOOKER.
Testimonial from Charles Darwin, Esq., M.A., F.R.S. and G.S., late Naturalist to Captain Fitz-Roy's Voyage.
Down House, Farnborough, August 25th, 1845.
I have heard with much interest that your son, Dr. Hooker, is a candidate for the Botanical Chair at Edinburgh. From my former attendance at that University, I am aware how important a post it is for the advancement of science, and I am therefore the more anxious for your son's success, from my firm belief that no one will fulfil its duties with greater zeal or ability. Since his return from the famous Antarctic expedition, I have had, as you are aware, much communication with him, with respect to the collections brought home by myself, and on other scientific subjects; and I cannot express too strongly my admiration at the accuracy of his varied knowledge, and at his powers of generalisation. From Dr. Hooker's disposition, no one, in my opinion, is more fitted to communicate to beginners a strong taste for those pursuits to which he is himself so ardently devoted. For the sake of the advancement of Botany in all its branches, your son has my warmest wishes for his success.
LETTER 581. TO J.D. HOOKER. Down, Thursday {June 11th, 1847}.
Many thanks for your kindness about the lodgings—it will be of great use to me. (581/1. The British Association met at Oxford in 1847.) Please let me know the address if Mr. Jacobson succeeds, for I think I shall go on the 22nd and write previously to my lodgings. I have since had a tempting invitation from Daubeny to meet Henslow, etc., but upon the whole, I believe, lodgings will answer best, for then I shall have a secure solitary retreat to rest in.
I am extremely glad I sent the Laburnum (581/2. This refers to the celebrated form known as Cytisus Adami, of which a full account is given in "Variation of Animals and Plants," Volume I., Edition II., page 413. It has been supposed to be a seminal hybrid or graft-hybrid between C. laburnum and C. purpureus. It is remarkable for bearing "on the same tree tufts of dingy red, bright yellow, and purple flowers, borne on branches having widely different leaves and manner of growth." In a paper by Camuzet in the "Annales de la Societe d'Horticulture de Paris, XIII., 1833, page 196, the author tries to show that Cytisus Adami is a seminal hybrid between C. alpinus and C. laburnum. Fuchs ("Sitz. k. Akad. Wien," Bd. 107) and Beijerinck ("K. Akad. Amsterdam," 1900) have spoken on Cytisus Adami, but throw no light on the origin of the hybrid. See letters to Jenner Weir in the present volume.): the raceme grew in centre of tree, and had a most minute tuft of leaves, which presented no unusual appearance: there is now on one raceme a terminal bilateral {i.e., half yellow, half purple} flower, and on other raceme a single terminal pure yellow and one adjoining bilateral flower. If you would like them I will send them; otherwise I would keep them to see whether the bilateral flowers will seed, for Herbert (581/3. Dean Herbert.) says the yellow ones will. Herbert is wrong in thinking there are no somewhat analogous facts: I can tell you some, when we meet. I know not whether botanists consider each petal and stamen an individual; if so, there seems to me no especial difficulty in the case, but if a flower-bud is a unit, are not their flowers very strange?
I have seen Dillwyn in the "Gardeners' Chronicle," and was disgusted at it, for I thought my bilateral flowers would have been a y for you.
(581/4. In a letter to Hooker, dated June 2nd, 1847, Darwin makes a bold suggestion as to floral symmetry:—)
I send you a tuft of the quasi-hybrid Laburnum, with two kinds of flowers on same stalk, and with what strikes {me} as very curious (though I know it has been observed before), namely, a flower bilaterally different: one other, I observe, has half its calyx purple. Is this not very curious, and opposed to the morphological idea that a flower is a condensed continuous spire of leaves? Does it not look as if flowers were normally bilateral; just in the same way as we now know that the radiating star-fish, etc., are bilateral? The case reminds me of those insects with exactly half having secondary male characters and the other half female.
(581/5. It is interesting to note his change of view in later years. In an undated letter written to Mr. Spencer, probably in 1873, he says: "With respect to asymmetry in the flowers themselves, I remain contented, from all that I have seen, with adaptation to visits of insects. There is, however, another factor which it is likely enough may have come into play—viz., the protection of the anthers and pollen from the injurious effects of rain. I think so because several flowers inhabiting rainy countries, as A. Kerner has lately shown, bend their heads down in rainy weather.")
LETTER 582. TO J.D. HOOKER. June {1855}.
(582/1. This is an early example of Darwin's interest in the movements of plants. Sleeping plants, as is well-known, may acquire a rhythmic movement differing from their natural period, but the precise experiment here described has not, as far as known, been carried out. See Pfeffer, "Periodische Bewegungen," 1875, page 32.)
I thank you much for Hedysarum: I do hope it is not very precious, for, as I told you, it is for probably a most foolish purpose. I read somewhere that no plant closes its leaves so promptly in darkness, and I want to cover it up daily for half an hour, and see if I can TEACH IT to close by itself, or more easily than at first in darkness. I am rather puzzled about its transmission, from not knowing how tender it is...
LETTER 583. TO J.D. HOOKER. Down, July 19th, 1856.
I thank you warmly for the very kind manner with which you have taken my request. It will, in truth, be a most important service to me; for it is absolutely necessary that I should discuss single and double creations, as a very crucial point on the general origin of species, and I must confess, with the aid of all sorts of visionary hypotheses, a very hostile one. I am delighted that you will take up possibility of crossing, no botanist has done so, which I have long regretted, and I am glad to see that it was one of A. De Candolle's desiderata. By the way, he is curiously contradictory on subject. I am far from expecting that no cases of apparent impossibility will be found; but certainly I expect that ultimately they will disappear; for instance, Campanulaceae seems a strong case, but now it is pretty clear that they must be liable to crossing. Sweet-peas (583/1. In Lathyrus odoratus the absence of the proper insect has been supposed to prevent crossing. See "Variation under Domestication," Edition II., Volume II., page 68; but the explanation there given for Pisum may probably apply to Lathyrus.), bee-orchis, and perhaps hollyhocks are, at present, my greatest difficulties; and I find I cannot experimentise by castrating sweet-peas, without doing fatal injury. Formerly I felt most interest on this point as one chief means of eliminating varieties; but I feel interest now in other ways. One general fact {that} makes me believe in my doctrine (583/2. The doctrine which has been epitomised as "Nature abhors perpetual self-fertilisation," and is generally known as Knight's Law or the Knight-Darwin Law, is discussed by Francis Darwin in "Nature," 1898. References are there given to the chief passages in the "Origin of Species," etc., bearing on the question. See Letter 19, Volume I.), is that NO terrestrial animal in which semen is liquid is hermaphrodite except with mutual copulation; in terrestrial plants in which the semen is dry there are many hermaphrodites. Indeed, I do wish I lived at Kew, or at least so that I could see you oftener. To return again to subject of crossing: I have been inclined to speculate so far, as to think (my!?) notion (I say MY notion, but I think others have put forward nearly or quite similar ideas) perhaps explains the frequent separation of the sexes in trees, which I think I have heard remarked (and in looking over the mono- and dioecious Linnean classes in Persoon seems true) are very apt to have sexes separated; for {in} a tree having a vast number of flowers on the same individual, or at least the same stock, each flower, if only hermaphrodite on the common plan, would generally get its own pollen or only pollen from another flower on same stock,—whereas if the sexes were separate there would be a better chance of occasional pollen from another distinct stock. I have thought of testing this in your New Zealand Flora, but I have no standard of comparison, and I found myself bothered by bushes. I should propound that some unknown causes had favoured development of trees and bushes in New Zealand, and consequent on this there had been a development of separation of sexes to prevent too much intermarriage. I do not, of course, suppose the prevention of too much intermarriage the only good of separation of sexes. But such wild notions are not worth troubling you with the reading of.
LETTER 584. TO J.D. HOOKER. Moor Park {May 2nd, 1857}.
The most striking case, which I have stumbled on, on apparent, but false relation of structure of plants to climate, seems to be Meyer and Doege's remark that there is not one single, even moderately-sized, family at the Cape of Good Hope which has not one or several species with heath-like foliage; and when we consider this together with the number of true heaths, any one would have been justified, had it not been for our own British heaths (584/1. It is well known that plants with xerophytic characteristics are not confined to dry climates; it is only necessary to mention halophytes, alpine plants and certain epiphytes. The heaths of Northern Europe are placed among the xerophytes by Warming ("Lehrbuch der okologischen Pflanzengeographie," page 234, Berlin, 1896).), in saying that heath-like foliage must stand in direct relation to a dry and moderately warm climate. Does this not strike you as a good case of false relation? I am so pleased with this place and the people here, that I am greatly tempted to bring Etty here, for she has not, on the whole, derived any benefit from Hastings. With thanks for your never failing assistance to me...
I remember that you were surprised at number of seeds germinating in pond mud. I tried a fourth pond, and took about as much mud (rather more than in former case) as would fill a very large breakfast cup, and before I had left home 118 plants had come up; how many more will be up on my return I know not. This bears on chance of birds by their muddy feet transporting fresh-water plants.
This would not be a bad dodge for a collector in country when plants were not in seed, to collect and dry mud from ponds.
LETTER 585. TO ASA GRAY. Down {1857}.
I am very glad to hear that you think of discussing the relative ranges of the identical and allied U. States and European species, when you have time. Now this leads me to make a very audacious remark in opposition to what I imagine Hooker has been writing (585/1. See Letter 338, Volume I.), and to your own scientific conscience. I presume he has been urging you to finish your great "Flora" before you do anything else. Now I would say it is your duty to generalise as far as you safely can from your as yet completed work. Undoubtedly careful discrimination of species is the foundation of all good work; but I must look at such papers as yours in Silliman as the fruit. As careful observation is far harder work than generalisation, and still harder than speculation, do you not think it very possible that it may be overvalued? It ought never to be forgotten that the observer can generalise his own observations incomparably better than any one else. How many astronomers have laboured their whole lives on observations, and have not drawn a single conclusion; I think it is Herschel who has remarked how much better it would be if they had paused in their devoted work and seen what they could have deduced from their work. So do pray look at this side of the question, and let us have another paper or two like the last admirable ones. There, am I not an audacious dog!
You ask about my doctrine which led me to expect that trees would tend to have separate sexes. I am inclined to believe that no organic being exists which perpetually self-fertilises itself. This will appear very wild, but I can venture to say that if you were to read my observations on this subject you would agree it is not so wild as it will at first appear to you, from flowers said to be always fertilised in bud, etc. It is a long subject, which I have attended to for eighteen years. Now, it occurred to me that in a large tree with hermaphrodite flowers, we will say it would be ten to one that it would be fertilised by the pollen of its own flower, and a thousand or ten thousand to one that if crossed it would be crossed only with pollen from another flower of same tree, which would be opposed to my doctrine. Therefore, on the great principle of "Nature not lying," I fully expected that trees would be apt to be dioecious or monoecious (which, as pollen has to be carried from flower to flower every time, would favour a cross from another individual of the same species), and so it seems to be in Britain and New Zealand. Nor can the fact be explained by certain families having this structure and chancing to be trees, for the rule seems to hold both in genera and families, as well as in species.
I give you full permission to laugh your fill at this wild speculation; and I do not pretend but what it may be chance which, in this case, has led me apparently right. But I repeat that I feel sure that my doctrine has more probability than at first it appears to have. If you had not asked, I should not have written at such length, though I cannot give any of my reasons.
The Leguminosae are my greatest opposers: yet if I were to trust to observations on insects made during many years, I should fully expect crosses to take place in them; but I cannot find that our garden varieties ever cross each other. I do NOT ask you to take any trouble about it, but if you should by chance come across any intelligent nurseryman, I wish you would enquire whether they take any pains in raising the varieties of papilionaceous plants apart to prevent crossing. (I have seen a statement of naturally formed crossed Phaseoli near N. York.) The worst is that nurserymen are apt to attribute all varieties to crossing.
Finally I incline to believe that every living being requires an occasional cross with a distinct individual; and as trees from the mere multitude of flowers offer an obstacle to this, I suspect this obstacle is counteracted by tendency to have sexes separated. But I have forgotten to say that my maximum difficulty is trees having papilionaceous flowers: some of them, I know, have their keel-petals expanded when ready for fertilisation; but Bentham does not believe that this is general: nevertheless, on principle of nature not lying, I suspect that this will turn out so, or that they are eminently sought by bees dusted with pollen. Again I do NOT ask you to take trouble, but if strolling under your Robinias when in full flower, just look at stamens and pistils whether protruded and whether bees visit them. I must just mention a fact mentioned to me the other day by Sir W. Macarthur, a clever Australian gardener: viz., how odd it was that his Erythrinas in N.S. Wales would not set a seed, without he imitated the movements of the petals which bees cause. Well, as long as you live, you will never, after this fearfully long note, ask me why I believe this or that.
LETTER 586. TO ASA GRAY. June 18th {1857}.
It has been extremely kind of you telling me about the trees: now with your facts, and those from Britain, N. Zealand, and Tasmania I shall have fair materials for judging. I am writing this away from home, but I think your fraction of 95/132 is as large as in other cases, and is at least a striking coincidence.
I thank you much for your remarks about my crossing notions, to which, I may add, I was led by exactly the same idea as yours, viz., that crossing must be one means of eliminating variation, and then I wished to make out how far in animals and vegetables this was possible. Papilionaceous flowers are almost dead floorers to me, and I cannot experimentise, as castration alone often produces sterility. I am surprised at what you say about Compositae and Gramineae. From what I have seen of latter they seemed to me (and I have watched wheat, owing to what L. de Longchamps has said on their fertilisation in bud) favourable for crossing; and from Cassini's observations and Kolreuter's on the adhesive pollen, and C.C. Sprengel's, I had concluded that the Compositae were eminently likely (I am aware of the pistil brushing out pollen) to be crossed. (586/1. This is an instance of the curious ignorance of the essential principles of floral mechanism which was to be found even among learned and accomplished botanists such as Gray, before the publication of the "Fertilisation of Orchids." Even in 1863 we find Darwin explaining the meaning of dichogamy in a letter to Gray.) If in some months' time you can find time to tell me whether you have made any observations on the early fertilisation of plants in these two orders, I should be very glad to hear, as it would save me from great blunder. In several published remarks on this subject in various genera it has seemed to me that the early fertilisation has been inferred from the early shedding of the pollen, which I think is clearly a false inference. Another cause, I should think, of the belief of fertilisation in the bud, is the not-rare, abnormal, early maturity of the pistil as described by Gartner. I have hitherto failed in meeting with detailed accounts of regular and normal impregnation in the bud. Podostemon and Subularia under water (and Leguminosae) seem and are strongest cases against me, as far as I as yet know. I am so sorry that you are so overwhelmed with work; it makes your VERY GREAT kindness to me the more striking.
It is really pretty to see how effectual insects are. A short time ago I found a female holly sixty measured yards from any other holly, and I cut off some twigs and took by chance twenty stigmas, cut off their tops, and put them under the microscope: there was pollen on every one, and in profusion on most! weather cloudy and stormy and unfavourable, wind in wrong direction to have brought any.
LETTER 587. TO J.D. HOOKER. Down, January 12th {1858}.
I want to ask a question which will take you only few words to answer. It bears on my former belief (and Asa Gray strongly expressed opinion) that Papilionaceous flowers were fatal to my notion of there being no eternal hermaphrodites. First let me say how evidence goes. You will remember my facts going to show that kidney-beans require visits of bees to be fertilised. This has been positively stated to be the case with Lathyrus grandiflorus, and has been very partially verified by me. Sir W. Macarthur tells me that Erythrina will hardly seed in Australia without the petals are moved as if by bee. I have just met the statement that, with common bean, when the humble-bees bite holes at the base of the flower, and therefore cease visiting the mouth of the corolla, "hardly a bean will set." But now comes a much more curious statement, that {in} 1842-43, "since bees were established at Wellington (New Zealand), clover seeds all over the settlement, WHICH IT DID NOT BEFORE." (587/1. See Letter 362, Volume I.) The writer evidently has no idea what the connection can be. Now I cannot help at once connecting this statement (and all the foregoing statements in some degree support each other, as all have been advanced without any sort of theory) with the remarkable absence of Papilionaceous plants in N. Zealand. I see in your list Clianthus, Carmichaelia (four species), a new genus, a shrub, and Edwardsia (is latter Papilionaceous?). Now what I want to know is whether any of these have flowers as small as clover; for if they have large flowers they may be visited by humble-bees, which I think I remember do exist in New Zealand; and which humble-bees would not visit the smaller clover. Even the very minute little yellow clover in England has every flower visited and revisited by hive-bees, as I know by experience. Would it not be a curious case of correlation if it could be shown to be probable that herbaceous and small Leguminosae do not exist because when {their} seeds {are} washed ashore (!!!) no small bees exist there. Though this latter fact must be ascertained. I may not prove anything, but does it not seem odd that so many quite independent facts, or rather statements, should point all in one direction, viz., that bees are necessary to the fertilisation of Papilionaceous flowers?
LETTER 588. TO JOHN LUBBOCK (Lord Avebury). Sunday {1859}.
Do you remember calling my attention to certain flowers in the truss of Pelargoniums not being true, or not having the dark shade on the two upper petals? I believe it was Lady Lubbock's observation. I find, as I expected, it is always the central or sub-central flower; but what is far more curious, the nectary, which is blended with the peduncle of the flowers, gradually lessens and quite disappears (588/1. This fact is mentioned in Maxwell Masters' "Vegetable Teratology" (Ray Society's Publications), 1869, page 221.), as the dark shade on the two upper petals disappears. Compare the stalk in the two enclosed parcels, in each of which there is a perfect flower.
Now, if your gardener will not be outrageous, do look over your geraniums and send me a few trusses, if you can find any, having the flowers without the marks, sending me some perfect flowers on same truss. The case seems to me rather a pretty one of correlation of growth; for the calyx also becomes slightly modified in the flowers without marks.
LETTER 589. TO MAXWELL MASTERS. Down, April 7th {1860}.
I hope that you will excuse the liberty which I take in writing to you and begging a favour. I have been very much interested by the abstract (too brief) of your lecture at the Royal Institution. Many of the facts alluded to are full of interest for me. But on one point I should be infinitely obliged if you could procure me any information: namely, with respect to sweet-peas. I am a great believer in the natural crossing of individuals of the same species. But I have been assured by Mr. Cattell (589/1. The nurseryman he generally dealt with.), of Westerham, that the several varieties of sweet-pea can be raised close together for a number of years without intercrossing. But on the other hand he stated that they go over the beds, and pull up any false plant, which they very naturally attribute to wrong seeds getting mixed in the lot. After many failures, I succeeded in artificially crossing two varieties, and the offspring out of the same pod, instead of being intermediate, was very nearly like the two pure parents; yet in one, there was a trace of the cross, and these crossed peas in the next generation showed still more plainly their mongrel origin. Now, what I want to know is, whether there is much variation in sweet-peas which might be owing to natural crosses. What I should expect would be that they would keep true for many years, but that occasionally, perhaps at long intervals, there would be a considerable amount of crossing of the varieties grown close together. Can you give, or obtain from your father, any information on this head, and allow me to quote your authority? It would really be a very great favour and kindness.
LETTER 590. TO J.D. HOOKER.
(590/1. The genera Scaevola and Leschenaultia, to which the following letter refers, belong to the Goodeniaceae (Goodenovieae, Bentham Hooker), an order allied to the Lobeliaceae, although the mechanism of fertilisation resembles rather more nearly that of Campanula. The characteristic feature of the flower in this order is the indusium, or, as Delpino (590/2. Delpino's observations on Dichogamy, summarised by Hildebrand in "Bot. Zeitung," 1870, page 634.) calls it, the "collecting cup": this cuplike organ is a development of the style, and serves the same function as the hairs on the style of Campanula, namely, that of taking the pollen from the anthers and presenting it to the visiting insect. During this stage the immature stigma is at the bottom of the cup, and though surrounded by pollen is incapable of being pollinated. In most genera of the order the pollen is pushed out of the indusium by the growth of the style or stigma, very much as occurs in Lobelia or the Compositae. Finally the style emerges from the indusium (590/3. According to Hamilton ("Proc. Linn. Soc. N. S. Wales," X., 1895, page 361) the stigma rarely grows beyond the indusium in Dampiera. In the same journal (1885-6, page 157, and IX., 1894, page 201) Hamilton has given a number of interesting observations on Goodenia, Scaevola, Selliera, Brunonia. There seem to be mechanisms for cross- and also for self-fertilisation.), the stigmas open out and are pollinated from younger flowers. The mechanism of fertilisation has been described by F. Muller (590/4. In a letter to Hildebrand published in the "Bot. Zeitung," 1868, page 113.), and more completely by Delpino (loc. cit.).
Mr. Bentham wrote a paper (590/5. "Linn. Soc. Journal," 1869, page 203.) on the style and stigma in the Goodenovieae, where he speaks of Mr. Darwin's belief that fertilisation takes place outside the indusium. This statement, which we imagine Mr. Bentham must have had from an unpublished source, was incomprehensible to him as long as he confined his work to such genera as Goodenia, Scaevola, Velleia, Coelogyne, in which the mechanism is much as above described; but on examining Leschenaultia the meaning became clear. Bentham writes of this genus:—"The indusium is usually described as bry two-lipped, without any distinct stigma. The fact appears to be that the upper less prominent lip is stigmatic all over, inside and out, with a transverse band of short glandular hairs at its base outside, while the lower more prominent lip is smooth and glabrous, or with a tuft of rigid hairs. Perhaps this lower lip and the upper band of hairs are all that correspond to the indusium of other genera; and the so-called upper lip, outside of which impregnation may well take place, as observed by Mr. Darwin, must be regarded as the true stigma."
Darwin's interest in the Goodeniaceae was due to the mechanism being apparently fitted for self-fertilisation. In 1871 a writer signing himself F.W.B. made a communication to the "Gardeners' Chronicle" (590/6. 1871, page 1103.), in which he expresses himself as "agreeably surprised" to find Leschenaultia adapted for self-fertilisation, or at least for self-pollinisation. This led Darwin to publish a short note in the same journal, in which he describes the penetration of pollen-tubes into the viscid surface on the outside of the indusium. (590/7. 1871, page 1166. He had previously written in the "Journal of Horticulture and Cottage Gardener," May 28th, 1861, page 151:—"Leschenaultia formosa has apparently the most effective contrivance to prevent the stigma of one flower ever receiving a grain of pollen from another flower; for the pollen is shed in the early bud, and is there shut up round the stigma within a cup or indusium. But some observations led me to suspect that nevertheless insect agency here comes into play; for I found by holding a camel-hair pencil parallel to the pistil, and moving it as if it were a bee going to suck the nectar, the straggling hairs of the brush opened the lip of the indusium, entered it, stirred up the pollen, and brought out some grains. I did this to five flowers, and marked them. These five flowers all set pods; whereas only two other pods set on the whole plant, though covered with innumerable flowers...I wrote to Mr. James Drummond, at Swan River in Australia,...and he soon wrote to me that he had seen a bee cleverly opening the indusium and extracting pollen.") He also describes how a brush, pushed into the flower in imitation of an insect, presses "against the slightly projecting lower lip of the indusium, opens it, and some of the hairs enter and become smeared with pollen." The yield of pollen is therefore differently arranged in Leschenaultia; for in the more typical genera it depends on the growth of the style inside the indusium. Delpino, however (see Hildebrand's version, loc. cit.), describes a similar opening of the cup produced by pressure on the hairs in some genera of the order.)
Down, June 7th {1860}.
Best and most beloved of men, I supplicate and entreat you to observe one point for me. Remember that the Goodeniaceae have weighed like an incubus for years on my soul. It relates to Scaevola microcarpa. I find that in bud the indusium collects all the pollen splendidly, but, differently from Leschenaultia, cannot be afterwards easily opened. Further, I find that at an early stage, when the flower first opens, a boat-shaped stigma lies at the bottom of the indusium, and further that this stigma, after the flower has some time expanded, grows very rapidly, when the plant is kept hot, and pushes out of the indusium a mass of pollen; and at same time two horns project at the corners of the indusium. Now the appearance of these horns makes me suppose that these are the stigmatic surfaces. Will you look to this? for if they be by the relative position of the parts (with indusium and stigma bent at right angles to style) {I am led to think} that an insect entering a flower could not fail to have {its} whole back (at the period when, as I have seen, a whole mass of pollen is pushed out) covered with pollen, which would almost certainly get rubbed on the two horns. Indeed, I doubt whether, without this aid, pollen would get on to the horns. What interests me in the case is the analogy in result with the Lobelia, but by very different means. In Lobelia the stigma, before it is mature, pushes by its circular brush of hairs the pollen out of the conjoined anthers; here the indusium collects pollen, and then the growth of the stigma pushes it out. In the course of about 1 1/2 hour, I found an indusium with hairs on the outer edge perfectly clogged with pollen, and horns protruded, which before the 1 1/2 hour had not one grain of pollen outside the indusium, and no trace of protruding horns. So you will see how I wish to know whether the horns are the true stigmatic surfaces. I would try the case experimentally by putting pollen on the horns, but my greenhouse is so cold, and my plant so small, and in such a little pot, that I suppose it would not seed...
The little length of stigmatic horns at the moment when pollen is forced out of the indusium, compared to what they ultimately attain, makes me fancy that they are not then mature or ready, and if so, as in Lobelia, each flower must be fertilised by pollen from another and earlier flower.
How curious that the indusium should first so cleverly collect pollen and then afterwards push it out! Yet how closely analogous to Campanula brushing pollen out of the anther and retaining it on hairs till the stigma is ready. I am going to try whether Campanula sets seed without insect agency.
LETTER 591. TO J.D. HOOKER.
(591/1. The following letters are given here rather than in chronological order, as bearing on the Leschenaultia problem. The latter part of Letter 591 refers to the cleistogamic flowers of Viola.)
Down, May 1st {1862}.
If you can screw out time, do look at the stigma of the blue Leschenaultia biloba. I have just examined a large bud with the indusium not yet closed, and it seems to me certain that there is no stigma within. The case would be very important for me, and I do not like to trust solely to myself. I have been impregnating flowers, but it is rather difficult...
I have just looked again at Viola canina. The case is odder: only 2 stamens which embrace the stigma have pollen; the 3 other stamens have no anther-cells and no pollen. These 2 fertile anthers are of different shape from the 3 sterile others, and the scale representing the lower lip is larger and differently shaped from the 4 other scales representing 4 other petals.
In V. odorata (single flower) all five stamens produce pollen. But I daresay all this is known.
LETTER 592. TO J.D. HOOKER. November 3rd {1862}.
Do you remember the scarlet Leschenaultia formosa with the sticky margin outside the indusium? Well, this is the stigma—at least, I find the pollen-tubes here penetrate and nowhere else. What a joke it would be if the stigma is always exterior, and this by far the greatest difficulty in my crossing notions should turn out a case eminently requiring insect aid, and consequently almost inevitably ensuring crossing. By the way, have you any other Goodeniaceae which you could lend me, besides Leschenaultia and Scaevola, of which I have seen enough?
I had a long letter the other day from Crocker of Chichester; he has the real spirit of an experimentalist, but has not done much this summer.
LETTER 593. TO F. MULLER. Down, April 9th and 15th {1866}.
I am very much obliged by your letter of February 13th, abounding with so many highly interesting facts. Your account of the Rubiaceous plant is one of the most extraordinary that I have ever read, and I am glad you are going to publish it. I have long wished some one to observe the fertilisation of Scaevola, and you must permit me to tell you what I have observed. First, for the allied genus of Leschenaultia: utterly disbelieving that it fertilises itself, I introduced a camel-hair brush into the flower in the same way as a bee would enter, and I found that the flowers were thus fertilised, which never otherwise happens; I then searched for the stigma, and found it outside the indusium with the pollen-tubes penetrating it; and I convinced Dr. Hooker that botanists were quite wrong in supposing that the stigma lay inside the indusium. In Scaevola microcarpa the structure is very different, for the immature stigma lies at the base within the indusium, and as the stigma grows it pushes the pollen out of the indusium, and it then clings to the hairs which fringe the tips of the indusium; and when an insect enters the flower, the pollen (as I have seen) is swept from these long hairs on to the insect's back. The stigma continues to grow, but is not apparently ready for impregnation until it is developed into two long protruding horns, at which period all the pollen has been pushed out of the indusium. But my observations are here at fault, for I did not observe the penetration of the pollen-tubes. The case is almost parallel with that of Lobelia. Now, I hope you will get two plants of Scaevola, and protect one from insects, leaving the other uncovered, and observe the results, both in the number of capsules produced, and in the average number of seeds in each. It would be well to fertilise half a dozen flowers under the net, to prove that the cover is not injurious to fertility.
With respect to your case of Aristolochia, I think further observation would convince you that it is not fertilised only by larvae, for in a nearly parallel case of an Arum and a Aristolochia, I found that insects flew from flower to flower. I would suggest to you to observe any cases of flowers which catch insects by their probosces, as occurs with some of the Apocyneae (593/1. Probably Asclepiadeae. See H. Muller, "Fertilisation of Flowers," page 396.); I have never been able to conceive for what purpose (if any) this is effected; at the same time, if I tempt you to neglect your zoological work for these miscellaneous observations I shall be guilty of a great crime.
To return for a moment to the indusium: how curious it is that the pollen should be thus collected in a special receptacle, afterwards to be swept out by insects' agency!
I am surprised at what you tell me about the fewness of the flowers of your native orchids which produce seed-capsules. What a contrast with our temperate European species, with the exception of some species of Ophrys!—I now know of three or four cases of self-fertilising orchids, but all these are provided with means for an occasional cross.
I am sorry to say Dr. Cruger is dead from a fever.
I received yesterday your paper in the "Botanische Zeitung" on the wood of climbing plants. (593/2. Fritz Muller, "Ueber das Holz einiger um Desterro wachsenden Kletterpflanzen." "Botanische Zeitung," 1866, pages 57, 65.) I have read as yet only your very interesting and curious remarks on the subject as bearing on the change of species; you have pleased me by the very high compliments which you pay to my paper. I have been at work since March 1st on a new English edition (593/3. The 4th Edition.) of my "Origin," of which when published I will send you a copy. I have much regretted the time it has cost me, as it has stopped my other work. On the other hand, it will be useful for a new third German edition, which is now wanted. I have corrected it largely, and added some discussions, but not nearly so much as I wished to do, for, being able to work only two hours daily, I feared I should never get it finished. I have taken some facts and views from your work "Fur Darwin"; but not one quarter of what I should like to have quoted.
LETTER 594. TO A.G. MORE. Down, June 24th, 1860.
I hope that you will forgive the liberty which I take in writing to you and requesting a favour. Mr. H.C. Watson has given me your address, and has told me that he thought that you would be willing to oblige me. Will you please to read the enclosed, and then you will understand what I wish observed with respect to the bee-orchis. (594/1. Ophrys apifera.) What I especially wish, from information which I have received since publishing the enclosed, is that the state of the pollen-masses should be noted in flowers just beginning to wither, in a district where the bee-orchis is extremely common. I have been assured that in parts of Isle of Wight, viz., Freshwater Gate, numbers occur almost crowded together: whether anything of this kind occurs in your vicinity I know not; but, if in your power, I should be infinitely obliged for any information. As I am writing, I will venture to mention another wish which I have: namely, to examine fresh flowers and buds of the Aceras, Spiranthes, marsh Epipactis, and any other rare orchis. The point which I wish to examine is really very curious, but it would take too long space to explain. Could you oblige me by taking the great trouble to send me in an old tin canister any of these orchids, permitting me, of course, to repay postage? It would be a great kindness, but perhaps I am unreasonable to make such a request. If you will inform me whether you have leisure so far to oblige me, I would tell you my movements, for on account of my own health and that of my daughter, I shall be on the move for the next two or three weeks.
I am sure I have much cause to apologise for the liberty which I have taken...
LETTER 595. TO A.G. MORE. Down, August 3rd, 1860.
I thank you most sincerely for sending me the Epipactis {palustris}. You can hardly imagine what an interesting morning's work you have given me, as the rostellum exhibited a quite new modification of structure. It has been extremely kind of you to take so very much trouble for me. Have you looked at the pollen-masses of the bee-Ophrys? I do not know whether the Epipactis grows near to your house: if it does, and any object takes you to the place (pray do not for a moment think me so very unreasonable as to ask you to go on purpose), would you be so kind {as} to watch the flowers for a quarter of an hour, and mark whether any insects (and what?) visit these flowers.
I should suppose they would crawl in by depressing the terminal portion of the labellum; and that when within the flower this terminal portion would resume its former position; and lastly, that the insect in crawling out would not depress the labellum, but would crawl out at back of flower. (595/1. The observations of Mr. William Darwin on Epipactis palustris given in the "Fertilisation of Orchids," Edition II., 1877, page 99, bear on this point. The chief fertilisers are hive-bees, which are too big to crawl into the flower. They cling to the labellum, and by depressing it open up the entrance to the flower. Owing to the elasticity of the labellum and its consequent tendency to spring up when released, the bees, "as they left the flower, seemed to fly rather upwards." This agrees with Darwin's conception of the mechanism of the flower as given in the first edition of the Orchid 1862, page 100, although at that time he imagined that the fertilising insect crawled into the flower. The extreme flexibility and elasticity of the labellum was first observed by Mr. More (see first edition, page 99). The description of the flower given in the above letter to Mr. More is not quite clear; the reader is referred to the "Fertilisation of Orchids," loc. cit.) An insect crawling out of a recently opened flower would, I believe, have parts of the pollen-masses adhering to the back or shoulder. I have seen this in Listera. How I should like to watch the Epipactis.
If you can it any time send me Spiranthes or Aceras or O. ustulata, you would complete your work of kindness.
P.S.—If you should visit the Epipactis again, would you gather a few of the lower flowers which have been opened for some time and have begun to wither a little, and observe whether pollen is well cleared out of anther-case. I have been struck with surprise that in nearly all the lower flowers sent by you, though much of the pollen has been removed, yet a good deal of pollen is left wasted within the anthers. I observed something of this kind in Cephalanthera grandiflora. But I fear that you will think me an intolerable bore.
LETTER 596. TO A.G. MORE. Down, August 5th, 1860.
I am infinitely obliged for your most clearly stated observations on the bee-orchis. It is now perfectly clear that something removes the pollen-masses far more with you than in this neighbourhood. But I am utterly puzzled about the foot-stalk being so often cut through. I should suspect snails. I yesterday found thirty-nine flowers, and of them only one pollen-mass in three flowers had been removed, and as these were extremely much-withered flowers I am not quite sure of the truth of this. The wind again is a new element of doubt. Your observations will aid me extremely in coming to some conclusion. (596/1. Mr. More's observations on the percentage of flowers in which the pollinia were absent are quoted in "Fertilisation of Orchids," Edition I., page 68.) I hope in a day or two to receive some day-moths, on the probosces of which I am assured the pollen-masses of the bee-orchis still adhere (596/2. He was doomed to disappointment. On July 17th, 1861, he wrote to Mr. More:—"I found the other day a lot of bee-Ophrys with the glands of the pollinia all in their pouches. All facts point clearly to eternal self-fertilisation in this species; yet I cannot swallow the bitter pill. Have you looked at any this year?")...
I wrote yesterday to thank you for the Epipactis. For the chance of your liking to look at what I have found: take a recently opened flower, drag gently up the stigmatic surface almost any object (the side of a hooked needle), and you will find the cap of the hemispherical rostellum comes off with a touch, and being viscid on under-surface, clings to needle, and as pollen-masses are already attached to the back of rostellum, the needle drags out much pollen. But to do this, the curiously projecting and fleshy summits of anther-cases must at some time be pushed back slightly. Now when an insect's head gets into the flower, when the flap of the labellum has closed by its elasticity, the insect would naturally creep out by the back-side of the flower. And mark when the insect flies to another flower with the pollen-masses adhering to it, if the flap of labellum did not easily open and allow free ingress to the insect, it would surely rub off the pollen on the upper petals, and so not leave it on stigma. It is to know whether I have rightly interpreted the structure of this whole flower that I am so curious to see how insects act. Small insects, I daresay, would crawl in and out and do nothing. I hope that I shall not have wearied you with these details.
If you would like to see a pretty and curious little sight, look to Orchis pyramidalis, and you will see that the sticky glands are congenitally united into a saddle-shaped organ. Remove this under microscope by pincers applied to foot-stalk of pollen-mass, and look quickly at the spontaneous movement of the saddle-shaped organs and see how beautifully adapted to seize proboscis of moth.
LETTER 597. TO J.D. HOOKER December 4th {1860}.
Many thanks about Apocynum and Meyen.
The latter I want about some strange movements in cells of Drosera, which Meyen alone seems to have observed. (597/1. No observations of Meyen are mentioned in "Insectivorous Plants.") It is very curious, but Trecul disbelieves that Drosera really clasps flies! I should very much wish to talk over Drosera with you. I did chloroform it, and the leaves which were already expanded did not recover thirty seconds of exposure for three days. I used the expression weight for the bit of hair which caused movement and weighed 1/78000 of a grain; but I do not believe it is weight, and what it is, I cannot after many experiments conjecture. (597/2. The doubt here expressed as to whether the result is due to actual weight is interesting in connection with Pfeffer's remarkable discovery that a smooth object in contact with the gland produces no effect if the plant is protected from all vibration; on an ordinary table the slight shaking which reaches the plant is sufficient to make the body resting on the gland tremble, and thus produce a series of varying pressures—under these circumstances the gland is irritated, and the tentacle moves. See Pfeffer, "Untersuchungen aus d. bot. Institut zu Tubingen," Volume I., 1885, page 483; also "Insectivorous Plants," Edition II., page 22.) The movement in this case does not depend on the chemical nature of substance. Latterly I have tried experiments on single glands, and a microscopical atom of raw meat causes such rapid movement that I could see it move like hand of clock. In this case it is the nature of the object. It is wonderful the rapidity of the absorption: in ten seconds weak solution of carbonate of ammonia changes not the colour, but the state of contents within the glands. In two minutes thirty seconds juice of meat has been absorbed by gland and passed from cell to cell all down the pedicel (or hair) of the gland, and caused the sap to pass from the cells on the upper side of the pedicel to the lower side, and this causes the curvature of the pedicel. I shall work away next summer when Drosera opens again, for I am much interested in subject. After the glandular hairs have curved, the oddest changes take place—viz., a segregation of the homogeneous pink fluid and necessary slow movements in the thicker matter. By Jove, I sometimes think Drosera is a disguised animal! You know that I always so like telling you what I do, that you must forgive me scribbling on my beloved Drosera. Farewell. I am so very glad that you are going to reform your ways; I am sure that you would have injured your health seriously. There is poor Dana has done actually nothing—cannot even write a letter—for a year, and it is hoped that in another YEAR he may quite recover.
After this homily, good night, my dear friend. Good heavens, I ought not to scold you, but thank you, for writing so long and interesting a letter.
LETTER 598. TO E. CRESY. Down, December 12th {1860?}.
After writing out the greater part of my paper on Drosera, I thought of so many points to try, and I wished to re-test the basis of one large set of experiments, namely, to feel still more sure than I am, that a drop of plain water never produces any effect, that I have resolved to publish nothing this year. For I found in the record of my daily experiments one suspicious case. I must wait till next summer. It will be difficult to try any solid substances containing nitrogen, such as ivory; for two quite distinct causes excite the movement, namely, mechanical irritation and presence of nitrogen. When a solid substance is placed on leaf it becomes clasped, but is released sooner than when a nitrogenous solid is clasped; yet it is difficult (except with raw meat and flies) to be sure of the result, owing to differences in vigour of different plants. The last experiments which I tried before my plants became too languid are very curious, and were tried by putting microscopical atoms on the gland itself of single hairs; and it is perfectly evident that an atom of human hair, 1/76000 of a grain (as ascertained by weighing a length of hair) in weight, causes conspicuous movement. I do not believe (for atoms of cotton thread acted) it is the chemical nature; and some reasons make me doubt whether it is actual weight; it is not the shadow; and I am at present, after many experiments, confounded to know what the cause is. That these atoms did really act and alter the state of the contents of all the cells in the glandular hair, which moved, was perfectly clear. But I hope next summer to make out a good deal more...
LETTER 599. TO J.D. HOOKER. Down, May 14th {1861}.
I have been putting off writing from day to day, as I did not wish to trouble you, till my wish for a little news will not let me rest...
I have no news to tell you, for I have had no interesting letters for some time, and have not seen a soul. I have been going through the "Cottage Gardener" of last year, on account chiefly of Beaton's articles (599/1. Beaton was a regular contributor to the "Cottage Gardener," and wrote various articles on cross breeding, etc., in 1861. One of these was in reply to a letter published in the "Cottage Gardener," May 14th, 1861, page 112, in which Darwin asked for information as to the Compositae and the hollyhock being crossed by insect visitors. In the number for June 8th, 1861, page 211, Darwin wrote on the variability of the central flower of the carrot and the peloria of the central flower in Pelargonium. An extract from a letter by Darwin on Leschenaultia, "Cottage Gardener," May 28th, 1861, page 151, is given in Letter 590, note.); he strikes me as a clever but d—d cock-sure man (as Lord Melbourne said), and I have some doubts whether to be much trusted. I suspect he has never recorded his experiment at the time with care. He has made me indignant by the way he speaks of Gartner, evidently knowing nothing of his work. I mean to try and pump him in the "Cottage Gardener," and shall perhaps defend Gartner. He alludes to me occasionally, and I cannot tell with what spirit. He speaks of "this Mr. Darwin" in one place as if I were a very noxious animal.
Let me have a line about poor Henslow pretty soon.
(599/2. In a letter of May 18th, 1861, Darwin wrote again:—)
By the way, thanks about Beaton. I have now read more of his writings, and one answer to me in "Cottage Gardener." I can plainly see that he is not to be trusted. He does not well know his own subject of crossing.
LETTER 600. TO J.D. HOOKER.
(600/1. Part of this letter has been published in "Life and Letters," III., page 265.)
2, Hesketh Crescent, Torquay {1861}.
...The beauty of the adaptation of parts seems to me unparalleled. I should think or guess {that} waxy pollen was most differentiated. In Cypripedium, which seems least modified, and a much exterminated group, the grains are single. In all others, as far as I have seen, they are in packets of four; and these packets cohere into many wedge-formed masses in Orchis, into eight, four, and finally two. It seems curious that a flower should exist which could, at most, fertilise only two other flowers, seeing how abundant pollen generally is; this fact I look at as explaining the perfection of the contrivance by which the pollen, so important from its fewness, is carried from flower to flower. By the way, Cephalanthera has single pollen-grains, but this seems to be a case of degradation, for the rostellum is utterly aborted. Oddly, the columns of pollen are here kept in place by very early penetration of pollen-tubes into the edge of the stigma; nevertheless, it receives more pollen by insect agency. Epithecia {Dichaea} has done me one good little turn. I often speculated how the caudicle of Orchis had been formed. (600/2. The gradation here suggested is thoroughly worked out in the "Fertilisation of Orchids," Edition I., page 323, Edition II., page 257.) I had noticed slight clouds in the substance half way down; I have now dissected them out, and I find they are pollen-grains fairly embedded and useless. If you suppose the pollen-grains to abort in the lower half of the pollinia of Epipactis, but the parallel elastic threads to remain and cohere, you have the caudicle of Orchis, and can understand the few embedded and functionless pollen-grains. I must not look at any more exotic orchids: hearty thanks for your offer. But if you would make one single observation for me on Cypripedium, I should be glad. Asa Gray writes to me that the outside of the pollen-masses is sticky in this genus; I find that the whole mass consists of pollen-grains immersed in a sticky brownish thick fluid. You could tell by a mere lens and penknife. If it is, as I find it, pollen could not get on the stigma without insect aid. Cypripedium confounds me much. I conjecture that drops of nectar are secreted by the surface of the labellum beneath the anthers and in front of the stigma, and that the shield over the anthers and the form of labellum is to compel insects to insert their proboscis all round both organs. (600/3. This view was afterwards given up.) It would be troublesome for you to look at this, as it is always bothersome to catch the nectar secreting, and the cup of the labellum gets filled with water by gardener's watering.
I have examined Listera ovata, cordata, and Neottia nidus avis: the pollen is uniform; I suspect you must have seen some observation founded on a mistake from the penetration and hardening of sticky fluid from the rostellum, which does penetrate the pollen a little.
It is mere virtue which makes me not wish to examine more orchids; for I like it far better than writing about varieties of cocks and hens and ducks. Nevertheless, I have just been looking at Lindley's list in the "Vegetable Kingdom," and I cannot resist one or two of his great division of Arethuseae, which includes Vanilla. And as I know so well the Ophreae, I should like (God forgive me) any one of the Satyriadae, Disidae and Corycidae.
I fear my long lucubrations will have wearied you, but it has amused me to write, so forgive me.
LETTER 601. TO J.D. HOOKER.
(601/1. Part of the following letter is published in the "Life and Letters," the remainder, with the omission of part bearing on the Glen Roy problem, is now given as an example of the varied botanical assistance Darwin received from Sir Joseph Hooker. For the part relating to Verbascum see the "Variation of Animals and Plants," Edition II., 1875, Volume II., page 83. The point is that the white and yellow flowered plants which occur in two species of Verbascum are undoubted varieties, yet "the sterility which results from the crossing of the differently coloured varieties of the same species is fully as great as that which occurs in many cases when distinct species are crossed."
The sterility of the long-styled form (B) of Linum grandiflorum, with its own pollen is described in "Forms of Flowers," Edition II., page 87: his conclusions on the short-styled form (A) differ from those in the present letter.)
September 28th {1861}.
I am going to beg for help, and I will explain why I want it.
You offer Cypripedium; I should be very glad of a specimen, and of any good-sized Vandeae, or indeed any orchids, for this reason: I never thought of publishing separately, and therefore did not keep specimens in spirits, and now I should be very glad of a few woodcuts to illustrate my few remarks on exotic orchids. If you can send me any, send them by post in a tin canister on middle of day of Saturday, October 5th, for Sowerby will be here.
Secondly: Have you any white and yellow varieties of Verbascum which you could give me, or propagate for me, or LEND me for a year? I have resolved to try Gartner's wonderful and repeated statement, that pollen of white and yellow varieties, whether used on the varieties or on DISTINCT species, has different potency. I do not think any experiment can be more important on the origin of species; for if he is correct we certainly have what Huxley calls new physiological species arising. I should require several species of Verbascum besides the white and yellow varieties of the same species. It will be tiresome work, but if I can anyhow get the plants, it shall be tried.
Thirdly: Can you give me seeds of any Rubiaceae of the sub-order Cinchoneae, as Spermacoce, Diodia, Mitchella, Oldenlandia? Asa Gray says they present two forms like Primula. I am sure that this subject is well worth working out. I have just almost proved a very curious case in Linum grandiflorum which presents two forms, A and B. Pollen of A is perfectly fertile on stigma of A. But pollen of B is absolutely barren on its own stigma; you might as well put so much flour on it. It astounded me to see the stigmas of B purple with its own pollen; and then put a few grains of similar-looking pollen of A on them, and the germen immediately and always swelled; those not thus treated never swelling.
Fourthly: Can you give me any very hairy Saxifraga (for their functions) {i.e. the functions of the hairs}?
I send you a resume of my requests, to save you trouble. Nor would I ask for so much aid if I did not think all these points well worth trying to investigate.
My dear old friend, a letter from you always does me a world of good. And, the Lord have mercy on me, what a return I make.
LETTER 602. TO J.D. HOOKER. Down, October 4th {1861}.
Will you have the kindness to read the enclosed, and look at the diagram. Six words will answer my question. It is not an important point, but there is to me an irresistible charm in trying to make out homologies. (602/1. In 1880 he wrote to Mr. Bentham: "It was very kind of you to write to me about the Orchideae, for it has pleased me to an extreme degree that I could have been of the least use to you about the nature of the parts."—"Life and Letters," III., page 264.) You know the membranous cup or clinandrum, in many orchids, behind the stigma and rostellum: it is formed of a membrane which unites the filament of the normal dorsal anther with the edges of the pistil. The clinandrum is largely developed in Malaxis, and is of considerable importance in retaining the pollinia, which as soon as the flower opens are quite loose.
The appearance and similarity of the tissues, etc., at once gives suspicion that the lateral membranes of the clinandrum are the two other and rudimentary anthers, which in Orchis and Cephalanthera, etc., exist as mere papillae, here developed and utilised.
Now for my question. Exactly in the middle of the filament of the normal anther, and exactly in the middle of the lateral membrane of the clinandrum, and running up to the same height, are quite similar bundles of spiral vessels; ending upwards almost suddenly. Now is not this structure a good argument that I interpret the homologies of the sides of clinandrum rightly? (602/2. Though Robert Brown made use of the spiral vessels of orchids, yet according to Eichler, "Bluthendiagramme," 1875, Volume I., page 184, Darwin was the first to make substantial additions to the conclusions deducible from the course of the vessels in relation to the problem of the morphology of these plants. Eichler gives Darwin's diagram side by side with that of Van Tieghem without attempting to decide between the differences in detail by which they are characterised.)
I find that the great Bauer does not draw very correctly! (602/3. F. Bauer, whom Pritzel calls "der grosste Pflanzenmaler." The reference is to his "Illustrations of Orchidaceous Plants, with Notes and Prefatory Remarks by John Lindley," London, 1830-38, Folio. See "Fertilisation of Orchids," Edition II., page 82.) And, good Heavens, what a jumble he makes on functions.
LETTER 603. TO J.D. HOOKER. Down, October 22nd. {1861}.
Acropera is a beast,—stigma does not open, everything seems contrived that it shall NOT be anyhow fertilised. There is something very odd about it, which could only be made out by incessant watching on several individual plants.
I never saw the very curious flower of Canna; I should say the pollen was deposited where it is to prevent inevitable self-fertilisation. You have no time to try the smallest experiment, else it would be worth while to put pollen on some stigmas (supposing that it does not seed freely with you). Anyhow, insects would probably carry pollen from flower to flower, for Kurr states the tube formed by pistil, stamen and "nectarblatt" secretes (I presume internally) much nectar. Thanks for sending me the curious flower.
Now I want much some wisdom; though I must write at considerable length, your answer may be very brief.
(FIGURE 8.—FLORAL DIAGRAM OF AN ORCHID. The "missing bundle" could not be found in some species.)
In R. Brown's admirable paper in the "Linnean Transacts." (603/4. Volume XVI., page 685.) he suggests (and Lindley cautiously agrees) that the flower of orchids consists of five whorls, the inner whorl of the two whorls of anthers being all rudimentary, and when the labellum presents ridges, two or three of the anthers of both whorls {are} combined with it. In the ovarium there are six bundles of vessels: R. Brown judged by transverse sections. It occurred to me, after what you said, to trace the vessels longitudinally, and I have succeeded well. Look at my diagram {Figure 8} (which please return, for I am transported with admiration at it), which shows the vessels which I have traced, one bundle to each of fifteen theoretical organs, and no more. You will see the result is nothing new, but it seems to confirm strongly R. Brown, for I have succeeded (perhaps he did, but he does not say so) in tracing the vessels belonging to each organ in front of each other to the same bundle in the ovarium: thus the vessels going to the lower sepal, to the side of the labellum, and to one stigma (when there are two) all distinctly branch from one ovarian bundle. So in other cases, but I have not completely traced (only seen) that going to the rostellum. But here comes my only point of y: in all orchids as yet looked at (even one with so simple a labellum as Gymnadenia and Malaxis) the vessels on the two sides of the labellum are derived from the bundle which goes to the lower sepal, as in the diagram. This leads me to conclude that the labellum is always a compound organ. Now I want to know whether it is conceivable that the vessels coming from one main bundle should penetrate an organ (the labellum) which receives its vessels from another main bundle? Does it not imply that all that part of the labellum which is supplied by vessels coming from a lateral bundle must be part of a primordially distinct organ, however closely the two may have become united? It is curious in Gymnadenia to trace the middle anterior bundle in the ovarium: when it comes to the orifice of the nectary it turns and runs right down it, then comes up the opposite side and runs to the apex of the labellum, whence each side of the nectary is supplied by vessels from the bundles, coming from the lower sepals. Hence even the thin nectary is essentially, I infer, tripartite; hence its tendency to bifurcation at its top. This view of the labellum always consisting of three organs (I believe four when thick, as in Mormodes, at base) seems to me to explain its great size and tripartite form, compared with the other petals. Certainly, if I may trust the vessels, the simple labellum of Gymnadenia consists of three organs soldered together. Forgive me for writing at such length; a very brief answer will suffice. I am desperately interested in the subject: the destiny of the whole human race is as nothing to the course of vessels of orchids...
What plant has the most complex single stigma and pistil? The most complex I, in my ignorance, can think of is in Iris. I want to know whether anything beats in modification the rostellum of Catasetum. To-morrow I mean to be at Catasetum. Hurrah! What species is it? It is wonderfully different from that which Veitch sent me, which was C. saccatum.
According to the vessels, an orchid flower consists of three sepals and two petals free; and of a compound organ (its labellum), consisting of one petal and of two (or three) modified anthers; and of a second compound body consisting of three pistils, one normal anther, and two modified anthers often forming the sides of the clinandrum.
LETTER 604. TO JOHN LINDLEY.
(604/1. It was in the autumn of 1861 that Darwin made up his mind to publish his Orchid work as a rather than as a paper in the Linnean Society's "Journal." (604/2. See "Life and Letters," III., page 266.) The following letter shows that the new arrangement served as an incitement to fresh work.)
Down, October 25th {1861?}
Mr. James Veitch has been most generous. I did not know that you had spoken to him. If you see him pray say I am truly grateful; I dare not write to a live Bishop or a Lady, but if I knew the address of "Rucker"? and might use your name as introduction, I might write. I am half mad on the subject. Hooker has sent me many exotics, but I stopped him, for I thought I should make a fool of myself; but since I have determined to publish I much regret it.
(FIGURE 9.—HABENARIA CHLORANTHA (Longitudinal course of bundles).)
(605/1. The three upper curved outlines, two of which passing through the words "upper sepal," "upper petal," "lower sepal," were in red in the original; for explanation see text.)
This book is provided by FunNovel Novel Book | Fan Fiction Novel [Beautiful Free Novel Book]