From John Scott 16 January 1863
Edinburgh | Botanic Gardens
Jany. 16th. 1863.
The flowers of Lælia were all experimented upon ere I received your last, and there is no prospect of us having more of its section in flower for some time. I consequently cannot try the experiment you have lately suggested.1 I have, however, cut a portion of the column from two flowers of Lælia fertilised—as I had thought—by application of pollen-mass to rostellum.2 But I find I have been greatly deceived on an examination of these—by the mode at least in which this has been effected, though the pollen-mass was carefully applied to the latter organ. The difficulty which I anticipated in a former letter to you has presented itself in such a manner that I fear all our attempts at rostellic fertilisation will be baffled.3 A latent provisional force, an almost conscious sympathy—if I may so express myself—seems to exist between pollen and stigma, and is strikingly evoked, when these are not directly and normally applied to each other. There have we an interesting exhibition of that latent instinctive power, which nature has more or less lavishly bestowed upon vegetal Life, in anticipation of certain contingencies, by which she overcomes these, and enables the plant to perform its functional requirements. In the case under consideration, I find that in one of the columns a process extends itself from each of the stigmas—i.e. each side of stigmatic cavity—to the rostellum, and thus reaches the pollen-mass, into which the pollen-tubes insinuate themselves and are thus conducted into their normal route. In the other no such process is developed, nevertheless, the pollen-tubes are abundant in the conducting tissue of the style. Whether they extend themselves directly to the stigma; or pass along the anterior surface of the modified pistil—or rostellum—to it I cannot discover. I am inclined, to favour the former view, as I cannot find after a careful examination any trace of a pollen-tube passing down the anterior surface of rostellum to stigma; and I observed a single pollen-tube protruding quite freely from a grain upon rostellum towards the stigma. I am sorry that I have not examined some of these flowers earlier, as I might then have been able to speak more definitely. The latter case is not a little perplexing, as with the solitary exception I have mentioned, I can discover no trace now of pollen-tubes above the stigmatic-tissue where they most abruptly end abundantly.4 I will now attempt to describe a little more particularly one or two sections of them and you will perhaps suggest some means of preventing the recurrence of this deception, when I have an opportunity of experimenting upon Cattleya, and thus not let us again be so teasingly baffled, but force the tubes either to penetrate the rostellum, or remain inert, and thus satisfactorily show its real functional condition.5 I have an idea of applying a thickish solution of gum to stigma and allowing it to harden, before applying pollen-mass to rostellum.
In the column first referred to then, I find the stigmas and pollen-mass—the latter of course being applied to rostellum—connected by a firm yellowish process extended from the former part. This contains an abundance of elliptical and fusiform cells, similar to those found in the upper portion of the conducting tissue of the styles. It is surprising to see how these cells become elongated at times, when we follow them down the style, and how much they then resemble in certain respects the pollen tubes. Indeed, a hasty observer might almost pass them over for the latter were it not their closed extremities, and pale yellow nuclei. Their function is puzzling! Through this interpolated process then the pollen-tubes insinuate themselves and pass down into the style. Not a single tube is to be discovered in the tissue of rostellum. In the other column fertilisation is effected by a somewhat different process. There, I can discover no connection between pollen-grains and tubes, which nevertheless appear in great abundance in the stigmatic tissue. I made a number of sections of this column, to see if I could discover any trace of them along the anterior surface of rostellum, which I thought they might have passed along and then reached the stigma, but in vain. I therefore, know not whether of the conjectures I have already offered is the more probable, but this much I vouch, that there is an abundance of tubes in the style, and not one to be observed in the tissue of rostellum
I see in turning to your observations on the structure of the rostellum, that you remark on the absence of the coherent spindle-formed utriculi in that organ, and that this may probably account for its infertility.6 My experiments so far favour this view. I was perfectly ignorant of the opinion you there state, and was much puzzled with the occurrence of these peculiar cells, as none of the few works I have had an opportunity to consult mentioned even the existence of such. You have, however, afforded us a rich store in your treatise upon these plants; but I have not as yet had much time for digesting the structural portion;7 I have engaged my spare time principally with that explicating their varied means for fertilisation
I will be glad to afford you all the information I have on the subject of variation in plants,8 which I intended mentioning in my last9 had time permitted. And now I ask you to favour me with the nature of the information you require Is it simply lists of plants now presenting variations with us, or must I furnish you the history of each? If the former, I think I could furnish you with a number. That is supposing you to accept such changes as variegation of leaves, changes in colour of flower and the like. Have you done much amongst the Ferns in regard to variation, or do you intend treating upon them at all, as I see no allusion to them in “Origin”10 The facilities they afford for reproducing variations is wonderful and affords a strong argument in favour of the view I have proposed—‘on influence of sexual relations in transmitting variations”—11 May I take the liberty of asking you if any more probable explanation has occurred to you for their peculiar facility, than that I have proposed? For a time they almost exclusively engaged my attention. I will be glad to hear how you intend treating them.
I thank you for your promise, to remember with a copy of your paper on Linum.12 I am afraid my late paper on Drosera & Dionæa, will not be of much interest to you, such as it is however, I will send to you when printed, but they are very tardy in printing their ‘Proceedings’ here. As I see your name occasionally in the Gard. Chron. you may have observed a short notice of it in No. 2. 1863 under Bot. Soc. of Edin. 13
I am, Sir. J. Scott.
Experiments to cut Laelia stigma from rostellum and then to fertilise rostellum are baffled by "a latent instinctive power". Somehow the pollen-tubes find their way to the style.
Suggests CD study variation in ferns.
Please cite as
Darwin Correspondence Project, “Letter no. 3921,” accessed on 23 October 2016, http://www.darwinproject.ac.uk/DCP-LETT-3921