Volume Ii Part 38 (1/2)

Blumenau, Sa Catharina, Brazil, January 9th, 1881.

I do not know how to express [to] you my deep heartfelt grat.i.tude for the generous offer which you made to my brother on hearing of the late dreadful flood of the Itajahy. From you, dear sir, I should have accepted a.s.sistance without hesitation if I had been in need of it; but fortunately, though we had to leave our house for more than a week, and on returning found it badly damaged, my losses have not been very great.

I must thank you also for your wonderful book on the movements of plants, which arrived here on New Year's Day. I think n.o.body else will have been delighted more than I was with the results which you have arrived at by so many admirably conducted experiments and observations; since I observed the spontaneous revolving movement of Alisma I had seen similar movements in so many and so different plants that I felt much inclined to consider spontaneous revolving movement or circ.u.mnutation as common to all plants and the movements of climbing plants as a special modification of that general phenomenon. And this you have now convincingly, nay, superabundantly, proved to be the case.

I was much struck with the fact that with you Maranta did not sleep for two nights after having its leaves violently shaken by wind, for here we have very cold nights only after storms from the west or south-west, and it would be very strange if the leaves of our numerous species of Marantaceae should be prevented by these storms to a.s.sume their usual nocturnal position, just when nocturnal radiation was most to be feared.

It is rather strange, also, that Phaseolus vulgaris should not sleep during the early part of the summer, when the leaves are most likely to be injured during cold nights. On the contrary, it would not do any harm to many sub-tropical plants, that their leaves must be well illuminated during the day in order that they may a.s.sume at night a vertical position; for, in our climate at least, cold nights are always preceded by sunny days.

Of nearly allied plants sleeping very differently I can give you some more instances. In the genus Olyra (at least, in the one species observed by me) the leaves bend down vertically at night; now, in Endlicher's ”Genera plantarum” this genus immediately precedes Strephium, the leaves of which you saw rising vertically.

In one of two species of Phyllanthus, growing as weeds near my house, the leaves of the erect branches bend upwards at night, while in the second species, with horizontal branches, they sleep like those of Phyllanthus Niruri or of Ca.s.sia. In this second species the tips of the branches also are curled downwards at night, by which movement the youngest leaves are yet better protected. From their vertical nyct.i.tropic position the leaves of this Phyllanthus might return to horizontality, traversing 90 deg, in two ways, either to their own or to the opposite side of the branch; on the latter way no rotation would be required, while on the former each leaf must rotate on its own axis in order that its upper surface may be turned upwards. Thus the way to the wrong side appears to be even less troublesome. And indeed, in some rare cases I have seen three, four or even almost all the leaves of one side of a branch horizontally expanded on the opposite side, with their upper surfaces closely appressed to the lower surfaces of the leaves of that side.

This Phyllanthus agrees with Ca.s.sia not only in its manner of sleeping, but also by its leaves being paraheliotropic. (687/2. Paraheliotropism is the movement by which some leaves temporarily direct their edges to the source of light. See ”Movements of Plants,” page 445.) Like those of some Ca.s.siae its leaves take an almost perfectly vertical position, when at noon, on a summer day, the sun is nearly in the zenith; but I doubt whether this paraheliotropism will be observable in England. To-day, though continuing to be fully exposed to the sun, at 3 p.m. the leaves had already returned to a nearly horizontal position. As soon as there are ripe seeds I will send you some; of our other species of Phyllanthus I enclose a few seeds in this letter.

In several species of Hedychium the lateral halves of the leaves when exposed to bright suns.h.i.+ne, bend downwards so that the lateral margins meet. It is curious that a hybrid Hedychium in my garden shows scarcely any trace of this paraheliotropism, while both the parent species are very paraheliotropic.

Might not the inequality of the cotyledons of Citrus and of Pachira be attributed to the pressure, which the several embryos enclosed in the same seed exert upon each other? I do not know Pachira aquatica, but [in] a species, of which I have a tree in my garden, all the seeds are polyembryonic, and so were almost all the seeds of Citrus which I examined. With Coffea arabica also seeds including two embryos are not very rare; but I have not yet observed whether in this case the cotyledons be inequal.

I repeated to-day Duval-Jouve's measurements on Bryophyllum calycinum (687/3. ”Power of Movement in Plants,” page 237. F. Muller's measurements show, however, that there is a tendency in the leaves to be more highly inclined at night than in the middle of the day, and so far they agree with Duval-Jouve's results.); but mine did not agree with his; they are as follows:--

Distances in mm. between the tips of the upper pair of leaves.

January 9th, 1881 3 A.M. 1 P.M. 6 P.M.

1st plant 54 43 36 2nd plant 28 25 23 3rd plant 28 27 27 4th plant 51 46 39 5th plant 61 52 45 _______________________________________________

222 193 170

LETTER 688. TO F. MULLER. Down, February 23rd, 1881.

Your letter has interested me greatly, as have so many during many past years. I thought that you would not object to my publis.h.i.+ng in ”Nature”

(688/1. ”Nature,” March 3rd, 1881, page 409.) some of the more striking facts about the movements of plants, with a few remarks added to show the bearing of the facts. The case of the Phyllanthus (688/2. See Letter 687.), which turns up its leaves on the wrong side, is most extraordinary and ought to be further investigated. Do the leaflets sleep on the following night in the usual manner? Do the same leaflets on successive nights move in the same strange manner? I was particularly glad to hear of the strongly marked cases of paraheliotropism. I shall look out with much interest for the publication about the figs. (688/3.

F. Muller published on Caprification in ”Kosmos,” 1882.) The creatures which you sketch are marvellous, and I should not have guessed that they were hymenoptera. Thirty or forty years ago I read all that I could find about caprification, and was utterly puzzled. I suggested to Dr.

Cruger in Trinidad to investigate the wild figs, in relation to their cross-fertilisation, and just before he died he wrote that he had arrived at some very curious results, but he never published, as I believe, on the subject.

I am extremely glad that the inundation did not so greatly injure your scientific property, though it would have been a real pleasure to me to have been allowed to have replaced your scientific apparatus. (688/4.

See Letter 687.) I do not believe that there is any one in the world who admires your zeal in science and wonderful powers of observation more than I do. I venture to say this, as I feel myself a very old man, who probably will not last much longer.

P.S.--With respect to Phyllanthus, I think that it would be a good experiment to cut off most of the leaflets on one side of the petiole, as soon as they are asleep and vertically dependent; when the pressure is thus removed, the opposite leaflets will perhaps bend beyond their vertically dependent position; if not, the main petiole might be a little twisted so that the upper surfaces of the dependent and now unprotected leaflets should face obliquely the sky when the morning comes. In this case diaheliotropism would perhaps conquer the ordinary movements of the leaves when they awake, and [a.s.sume] their diurnal horizontal position. As the leaflets are alternate, and as the upper surface will be somewhat exposed to the dawning light, it is perhaps diaheliotropism which explains your extraordinary case.

LETTER 689. TO F. MULLER. Down, April 12th, 1881.

I have delayed answering your last letter of February 25th, as I was just sending to the printers the MS. of a very little book on the habits of earthworms, of which I will of course send you a copy when published.

I have been very much interested by your new facts on paraheliotropism, as I think that they justify my giving a name to this kind of movement, about which I long doubted. I have this morning drawn up an account of your observations, which I will send in a few days to ”Nature.” (689/1.

”Nature,” 1881, page 603. Curious facts are given on the movements of Ca.s.sia, Phyllanthus, sp., Desmodium sp. Ca.s.sia takes up a sunlight position unlike its own characteristic night-position, but resembling rather that of Haematoxylon (see ”Power of Movement,” figure 153, page 369). One species of Phyllanthus takes up in suns.h.i.+ne the nyct.i.tropic att.i.tude of another species. And the same sort of relation occurs in the genus Bauhinia.) I have thought that you would not object to my giving precedence to paraheliotropism, which has been so little noticed. I will send you a copy of ”Nature” when published. I am glad that I was not in too great a hurry in publis.h.i.+ng about Lagerstroemia. (689/2.

Lagerstraemia was doubtfully placed among the heterostyled plants (”Forms of Flowers,” page 167). F. Muller's observations showed that a totally different interpretation of the two sizes of stamen is possible.