Volume Ii Part 47 (1/2)

LETTER 761. TO J. LUBBOCK (Lord Avebury). Down, April 16th [1881].

Will you be so kind as to send and lend me the Desmodium gyrans by the bearer who brings this note.

Shortly after you left I found my notice of the seeds in the ”Gardeners'

Chronicle,” which please return hereafter, as I have no other copy.

(761/1. ”Note on the Achenia of Pumilio argyrolepis.” ”Gardeners'

Chronicle,” 1861, page 4.) I do not think that I made enough about the great power of absorption of water by the corolla-like calyx or pappus.

It seems to me not unlikely that the pappus of other Compositae may be serviceable to the seeds, whilst lying on the ground, by absorbing the dew which would be especially apt to condense on the fine points and filaments of the pappus. Anyhow, this is a point which might be easily investigated. Seeds of Tussilago, or groundsel (761/2. It is not clear whether Tussilago or groundsel (Senecio vulgaris) is meant; or whether he was not sure which of the two plants becomes slimy when wetted.), emit worm-like ma.s.ses of mucus, and it would be curious to ascertain whether wetting the pappus alone would suffice to cause such secretion.

(761/3. See Letter 707.)

LETTER 762. TO G.J. ROMANES. Down, April 18th, 1881.

I am extremely glad of your success with the flas.h.i.+ng light. (762/1.

Romanes' paper on the effect of intermittent light on heliotropism was the ”Proc. Royal Soc.” Volume LIV., page 333.) If plants are acted on by light, like some of the lower animals, there is an additional point of interest, as it seems to me, in your results. Most botanists believe that light causes a plant to bend to it in as direct a manner as light affects nitrate of silver. I believe that it merely tells the plant to which side to bend, and I see indications of this belief prevailing even with Sachs. Now it might be expected that light would act on a plant in something the same manner as on the lower animals. As you are at work on this subject, I will call your attention to another point. Wiesner, of Vienna (who has lately published a great book on heliotropism) finds that an intermittent light, say of 20 minutes, produces the same effect as a continuous light of, say 60 m. (762/2. Wiesner's papers on heliotropism are in the ”Denkschriften” of the Vienna Academy, Volumes 39 and 43.) So that Van Tieghem, in the first part of his book which has just appeared, remarks, the light during 40 m. out of the 60 m. produced no effect. I observed an a.n.a.logous case described in my book. (762/3.

”Power of Movement,” page 459.)

Wiesner and Van Tieghem seem to think that this is explained by calling the whole process ”induction,” borrowing a term used by some physico-chemists (of whom I believe Roscoe is one) and implying an agency which does not produce any effect for some time, and continues its effect for some time after the cause has ceased. I believe that photographic paper is an instance. I must ask Leonard (762/4. Mr.

Darwin's son.) whether an interrupted light acts on it in the same manner as on a plant. At present I must still believe in my explanation that it is the contrast between light and darkness which excites a plant.

I have forgotten my main object in writing--viz., to say that I believe (and have so stated) that seedlings vary much in their sensitiveness to light; but I did not prove this, for there are many difficulties, whether the time of incipient curvature or the amount of curvature is taken as the criterion. Moreover they vary according to age, and perhaps from vigour of growth, and there seems inherent variability, as Strasburger (whom I quote) found with spores. If the curious anomaly observed by you is due to varying sensitiveness, ought not all the seedlings to bend if the flashes were at longer intervals of time?

According to my notion of contrast between light and darkness being the stimulus, I should expect that if flashes were made sufficiently slow it would be a powerful stimulus, and that you would suddenly arrive at a period when the result would SUDDENLY become great. On the other hand, as far as my experience goes, what one expects rarely happens.

LETTER 763. TO JULIUS WIESNER. Down, October 4th, 1881.

I thank you sincerely for your very kind letter, and for the present of your new work. (763/1. ”Das Bewegungsvermogen der Pflanze,” 1881. One of us has given some account of Wiesner's book in the presidential address to Section D of the British a.s.sociation, 1891. Wiesner's divergence from Darwin's views is far-reaching, and includes the main thesis of the ”Power of Movement.” See ”Life and Letters,” III., page 336, for an interesting letter to Wiesner.) My son Francis, if he had been at home, would have likewise sent his thanks. I will immediately begin to read your book, and when I have finished it will write again. But I read german so very slowly that your book will take me a considerable time, for I cannot read for more than half an hour each day. I have, also, been working too hard lately, and with very little success, so that I am going to leave home for a time and try to forget science.

I quite expect that you will find some gross errors in my work, for you are a very much more skilful and profound experimentalist than I am.

Although I always am endeavouring to be cautious and to mistrust myself, yet I know well how apt I am to make blunders. Physiology, both animal and vegetable, is so difficult a subject, that it seems to me to progress chiefly by the elimination or correction of ever-recurring mistakes. I hope that you will not have upset my fundamental notion that various cla.s.ses of movement result from the modification of a universally present movement of circ.u.mnutation.

I am very glad that you will again discuss the view of the turgescence of the cells being the cause of the movement of parts. I adopted De Vries' views as seeming to me the most probable, but of late I have felt more doubts on this head. (763/2. See ”Power of Movement,” page 2. De Vries' work is published in the ”Bot. Zeitung,” 1879, page 830.)

LETTER 764. TO J.D. HOOKER. Glenrhydding House, Patterdale, Penrith, June 15th, 1881.

It was real pleasure to me to see once again your well-known handwriting on the outside of your note. I do not know how long you have returned from Italy, but I am very sorry that you are so bothered already with work and visits. I cannot but think that you are too kind and civil to visitors, and too conscientious about your official work. But a man cannot cure his virtues, any more than his vices, after early youth; so you must bear your burthen. It is, however, a great misfortune for science that you have so very little spare time for the ”Genera.” I can well believe what an awful job the palms must be. Even their size must be very inconvenient. You and Bentham must hate the monocotyledons, for what work the Orchideae must have been, and Gramineae and Cyperaceae will be. I am rather despondent about myself, and my troubles are of an exactly opposite nature to yours, for idleness is downright misery to me, as I find here, as I cannot forget my discomfort for an hour. I have not the heart or strength at my age to begin any investigation lasting years, which is the only thing which I enjoy; and I have no little jobs which I can do. So I must look forward to Down graveyard as the sweetest place on earth. This place is magnificently beautiful, and I enjoy the scenery, though weary of it; and the weather has been very cold and almost always hazy.

I am so glad that your tour has answered for Lady Hooker. We return home on the first week of July, and should be truly glad to aid Lady Hooker in any possible manner which she will suggest.

I have written to my gardener to send you plants of Oxalis corniculata (and seeds if possible). I should think so common a weed was never asked for before,--and what a poor return for the hundreds of plants which I have received from Kew! I hope that I have not bothered you by writing so long a note, and I did not intend to do so.

If Asa Gray has returned with you, please give him my kindest remembrances.

LETTER 765. TO J.D. HOOKER. October 22nd, 1881.