More Letters of Charles Darwin Volume Ii Part 41

(710/1. The following letters to Sir J.D. Hooker and the late Mr.

Moggridge refer to Moggridge's observation that seeds stored in the nest of the ant Atta at Mentone do not germinate, though they are certainly not dead. Moggridge's observations are given in his book, "Harvesting Ants and Trap-Door Spiders," 1873, which is full of interesting details.

The book is moreover remarkable in having resuscitated our knowledge of the existence of the seed-storing habit. Mr. Moggridge points out that the ancients were familiar with the facts, and quotes the well-known fable of the ant and the gra.s.shopper, which La Fontaine borrowed from Aesop. Mr. Moggridge (page 5) goes on: "So long as Europe was taught Natural History by southern writers the belief prevailed; but no sooner did the tide begin to turn, and the current of information to flood from north to south, than the story became discredited."

In Moggridge's "supplement" on the same subject, published in 1874, the author gives an account of his experiments made at Darwin's suggestion, and concludes (page 174) that "the vapour of formic acid is incapable of rendering the seeds dormant after the manner of the ants," and that indeed "its influence is always injurious to the seeds, even when present only in excessively minute quant.i.ties." Though unable to explain the method employed, he was convinced "that the non-germination of the seeds is due to some direct influence voluntarily exercised by the ants, and not merely to the conditions found in the nest" (page 172). See Volume I., Letter 251.)

Down, February 21st [1873].

You have given me exactly the information which I wanted.

Geniuses jump. I have just procured formic acid to try whether its vapour or minute drops will delay germination of fresh seeds; trying others at same time for comparison. But I shall not be able to try them till middle of April, as my despotic wife insists on taking a house in London for a month from the middle of March.

I am glad to hear of the Primer (710/2. "Botany" (Macmillan's Science Primers).); it is not at all, I think, a folly. Do you know Asa Gray's child book on the functions of plants, or some such t.i.tle? It is very good in giving an interest to the subject.

By the way, can you lend me the January number of the "London Journal of Botany" for an article on insect-agency in fertilisation?

LETTER 711. TO J. TRAHERNE MOGGRIDGE. Down, August 27th, 1873.

I thank you for your very interesting letter, and I honour you for your laborious and careful experiments. No one knows till he tries how many unexpected obstacles arise in subjecting plants to experiments.

I can think of no suggestions to make; but I may just mention that I had intended to try the effects of touching the dampened seeds with the minutest drop of formic acid at the end of a sharp gla.s.s rod, so as to imitate the possible action of the sting of the ant. I heartily hope that you may be rewarded by coming to some definite result; but I fail five times out of six in my own experiments. I have lately been trying some with poor success, and suppose that I have done too much, for I have been completely knocked up for some days.

LETTER 712. TO J. TRAHERNE MOGGRIDGE. Down, March 10th, 1874.

I am very sorry to hear that the vapour experiments have failed; but nothing could be better, as it seems to me, than your plan of enclosing a number of the ants with the seeds. The incidental results on the power of different vapours in killing seeds and stopping germination appear very curious, and as far as I know are quite new.

P.S.--I never before heard of seeds not germinating except during a certain season; it will be a very strange fact if you can prove this.

(712/1. Certain seeds pa.s.s through a resting period before germination.

See Pfeffer's "Pflanzenphysiologie," Edition I., Volume II., page III.)

LETTER 713. TO H. MULLER. Down, May 30th, 1873.

I am much obliged for your letter received this morning. I write now chiefly to give myself the pleasure of telling you how cordially I admire the last part of your book, which I have finished. (713/1.

"Die Befruchtung der Blumen durch Insekten": Leipzig, 1873. An English translation was published in 1883 by Prof. D'Arcy Thompson. The "Prefatory Notice" to this work (February 6th, 1882) is almost the last of Mr. Darwin's writings. See "Life and Letters," page 281.) The whole discussion seems to me quite excellent, and it has pleased me not a little to find that in the rough MS. of my last chapter I have arrived on many points at nearly the same conclusions that you have done, though we have reached them by different routes. (713/2. "The Effects of Cross and Self-Fertilisation in the Vegetable Kingdom": London, 1876.)

LETTER 714. TO F. DELPINO. Down, June 25th [1873].

I thank you sincerely for your letter. I am very glad to hear about Lathyrus odoratus, for here in England the vars. never cross, and yet are sometimes visited by bees. (714/1. In "Cross and Self-Fertilisation," page 156, Darwin quotes the information received from Delpino and referred to in the present letter--namely, that it is the fixed opinion of the Italian gardeners that the varieties do intercross. See Letter 709.) Pisum sativum I have also many times seen visited by Bombus. I believe the cause of the many vars. not crossing is that under our climate the flowers are self-fertilised at an early period, before the corolla is fully expanded. I shall examine this point with L. odoratus. I have read H. Muller's book, and it seems to me very good. Your criticism had not occurred to me, but is, I think just--viz.

that it is much more important to know what insects habitually visit any flower than the various kinds which occasionally visit it. Have you seen A. Kerner's book "Schutzmittel des Pollens," 1873, Innsbruck. (714/2.

Afterwards translated by Dr. Ogle as "Flowers and their Unbidden Guests," with a prefatory letter by Charles Darwin, 1878.) It is very interesting, but he does not seem to know anything about the work of other authors.

I have Bentham's paper in my house, but have not yet had time to read a word of it. He is a man with very sound judgment, and fully admits the principle of evolution.

I have lately had occasion to look over again your discussion on anemophilous plants, and I have again felt much admiration at your work.

(714/3. "Atti della Soc. Italiana di Scienze Nat." Volume XIII.)

(714/4. In the beginning of August, 1873, Darwin paid the first of several visits to Lord Farrer's house at Abinger. When sending copies of Darwin's letters for the "Life and Letters," Lord Farrer was good enough to add explanatory notes and recollections, from which we quote the following sketch.)

"Above my house are some low hills, standing up in the valley, below the chalk range on the one hand and the more distant range of Leith Hill on the other, with pretty views of the valley towards Dorking in one direction and Guildford in the other. They are composed of the less fertile Greensand strata, and are covered with fern, broom, gorse, and heath. Here it was a particular pleasure of his to wander, and his tall figure, with his broad-brimmed Panama hat and long stick like an alpenstock, sauntering solitary and slow over our favourite walks, is one of the pleasantest of the many pleasant a.s.sociations I have with the place."

LETTER 715. TO T.H. FARRER (Lord Farrer).

(715/1. The following note by Lord Farrer explains the main point of the letter, which, however, refers to the "bloom" problem as well as to Coronilla:--

"I thought I had found out what puzzled us in Coronilla varia: in most of the Papilionaceae, when the tenth stamen is free, there is nectar in the staminal tube, and the opening caused by the free stamen enables the bee to reach the nectar, and in so doing the bee fertilises the plant.

In Coronilla varia, and in several other species of Coronilla, there is no nectar in the staminal tube or in the tube of the corolla. But there are peculiar glands with nectar on the outside of the calyx, and peculiar openings in the tube of the corolla through which the proboscis of the bee, whilst entering the flower in the usual way and dusting itself with pollen, can reach these glands, thus fertilising the plant in getting the nectar. On writing this to Mr. Darwin, I received the following characteristic note.

The first postscript relates to the rough ground behind my house, over which he was fond of strolling. It had been ploughed up and then allowed to go back, and the interest was to watch how the numerous species of weeds of cultivation which followed the plough gradually gave way in the struggle for existence to the well-known and much less varied flora of an English common.")

Ba.s.sett, Southampton, August 14th, 1873.

You are the man to conquer a Coronilla. (715/2. In a former letter to Lord Farrer, Darwin wrote: "Here is a maxim for you, 'It is disgraceful to be beaten by a Coronilla.'") I have been looking at the half-dried flowers, and am prepared to swear that you have solved the mystery.

The difference in the size of the cells on the calyx under the vexillum right down to the common peduncle is conspicuous. The flour still adhered to this side; I see little bracteae or stipules apparently with glandular ends at the base of the calyces. Do these secrete? It seems to me a beautiful case. When I saw the odd shape of the base of the vexillum, I concluded that it must have some meaning, but little dreamt what that was. Now there remains only the one serious point--viz.the separation of the one stamen. I daresay that you are right in that nectar was originally secreted within the staminal tube; but why has not the one stamen long since cohered? The great difference in structure for fertilisation within the same genus makes one believe that all such points are vary variable. (715/3. Coronilla emerus is of the ordinary papilionaceous type.) With respect to the non-coherence of the one stamen, do examine some flower-buds at a very early age; for parts which are largely developed are often developed to an unusual degree at a very early age, and it seems to me quite possible that the base of the vexillum (to which the single stamen adhered) might thus be developed, and thus keep it separate for a time from the other stamens. The cohering stamens to the right and left of the single one seem to me to be pushed out a little laterally. When you have finished your observations, you really ought to send an account with a diagram to "Nature," recalling your generalisation about the diadelphous structure, and now explaining the exception of Coronilla. (715/4. The observations were published in "Nature," Volume X., 1874, page 169.)

Do add a remark how almost every detail of structure has a meaning where a flower is well examined.

Your observations pleased me so much that I could not sit still for half an hour.

Please to thank Mr. Payne (715/5. Lord Farrer's gardener.) for his remarks, which are of value to me, with reference to Mimosa. I am very much in doubt whether opening the sashes can act by favouring the evaporation of the drops; may not the movement of the leaves shake off the drops, or change their places? If Mr. Payne remembers any plant which is easily injured by drops, I wish he would put a drop or two on a leaf on a bright day, and cover the plant with a clean bell-gla.s.s, and do the same for another plant, but without a bell-gla.s.s over it, and observe the effects.

Thank you much for wis.h.i.+ng to see us again at Abinger, and it is very doubtful whether it will be Coronilla, Mr. Payne, the new garden, the children, E. [Lady Farrer], or yourself which will give me the most pleasure to see again.

P.S. 1.--It will be curious to note in how many years the rough ground becomes quite uniform in its flora.

P.S. 2.--One may feel sure that periodically nectar was secreted within the flower and then secreted by the calyx, as in some species of Iris and orchids. This latter being taken advantage of in Coronilla would allow of the secretion within the flower ceasing, and as this change was going on in the two secretions, all the parts of the flower would become modified and correlated.

LETTER 716. TO J. BURDON SANDERSON. Down, Tuesday, September 9th [1873].

(716/1. Sir J. Burdon Sanderson showed that in Dionoea movement is accompanied by electric disturbances closely a.n.a.logous to those occurring in muscle (see "Nature," 1874, pages 105, 127; "Proc. R. Soc."

XXI., and "Phil. Trans." Volume CLXXIII., 1883, where the results are finally discussed).)

I will send up early to-morrow two plants [of Dionoea] with five goodish leaves, which you will know by their being tied to sticks. Please remember that the slightest touch, even by a hair, of the three filaments on each lobe makes the leaf close, and it will not open for twenty-four hours. You had better put 1/4 in. of water into the saucers of the pots. The plants have been kept too cool in order to r.e.t.a.r.d them. You had better keep them rather warm (i.e. temperature of warm greenhouse) for a day, and in a good light.

I am extremely glad you have undertaken this subject. If you get a positive result, I should think you ought to publish it separately, and I could quote it; or I should be most glad to introduce any note by you into my account.

I have no idea whether it is troublesome to try with the thermo-electric pile any change of temperature when the leaf closes. I could detect none with a common thermometer. But if there is any change of temperature I should expect it would occur some eight to twelve or twenty-four hours after the leaf has been given a big smashed fly, and when it is copiously secreting its acid digestive fluid.

I forgot to say that, as far as I can make out, the inferior surface of the leaf is always in a state of tension, and that the contraction is confined to the upper surface; so that when this contraction ceases or suddenly fails (as by immersion in boiling water) the leaf opens again, or more widely than is natural to it.

Whenever you have quite finished, I will send for the plants in their basket. My son Frank is staying at 6, Queen Anne Street, and comes home on Sat.u.r.day afternoon, but you will not have finished by that time.

P.S. I have repeated my experiment on digestion in Drosera with complete success. By giving leaves a very little weak hydrochloric acid, I can make them digest alb.u.men--i.e. white of egg--quicker than they can do naturally. I most heartily thank you for all your kindness. I have been pretty bad lately, and must work very little.