第381章

Pray believe me, dear Professor Semper, Yours sincerely, CHARLES DARWIN.

GALLS.

[Shortly before his death, my father began to experimentise on the possibility of producing galls artificially. A letter to Sir J.D. Hooker (November 3, 1880) shows the interest which he felt in the question:--"I was delighted with Paget's Essay ('Disease in Plants,' by Sir James Paget.--See "Gardeners' Chronicle", 1880.); I hear that he has occasionally attended to this subject from his youth...I am very glad he has called attention to galls: this has always seemed to me a profoundly interesting subject; and if I had been younger would take it up."His interest in this subject was connected with his ever-present wish to learn something of the causes of variation. He imagined to himself wonderful galls caused to appear on the ovaries of plants, and by these means he thought it possible that the seed might be influenced, and thus new varieties arise. He made a considerable number of experiments by injecting various reagents into the tissues of leaves, and with some slight indications of success.]

AGGREGATION.

[The following letter gives an idea of the subject of the last of his published papers. ('Journal of the Linnean Society.' volume xix, 1882, pages 239 and 262.) The appearances which he observed in leaves and roots attracted him, on account of their relation to the phenomena of aggregation which had so deeply interested him when he was at work on Drosera:]

CHARLES DARWIN TO S.H. VINES. (Reader in Botany in the University of Cambridge.)Down, November 1, 1881.

My dear Mr. Vines, As I know how busy you are, it is a great shame to trouble you. But you are so rich in chemical knowledge about plants, and I am so poor, that Iappeal to your charity as a pauper. My question is--Do you know of any solid substance in the cells of plants which glycerine and water dissolves?

But you will understand my perplexity better if I give you the facts: Imentioned to you that if a plant of Euphorbia peplus is gently dug up and the roots placed for a short time in a weak solution (1 to 10,000 of water, suffices in 24 hours) of carbonate of ammonia the (generally) alternate longitudinal rows of cells in every rootlet, from the root-cap up to the very top of the root (but not as far as I have yet seen in the green stem)become filled with translucent, brownish grains of matter. These rounded grains often cohere and even become confluent. Pure phosphate and nitrate of ammonia produce (though more slowly) the same effect, as does pure carbonate of soda.

Now, if slices of root under a cover-glass are irrigated with glycerine and water, every one of the innumerable grains in the cells disappear after some hours. What am I to think of this.?...

Forgive me for bothering you to such an extent; but I must mention that if the roots are dipped in boiling water there is no deposition of matter, and carbonate of ammonia afterwards produces no effect. I should state that Inow find that the granular matter is formed in the cells immediately beneath the thin epidermis, and a few other cells near the vascular tissue.

If the granules consisted of living protoplasm (but I can see no traces of movement in them), then I should infer that the glycerine killed them and aggregation ceased with the diffusion of invisibly minute particles, for Ihave seen an analogous phenomenon in Drosera.

If you can aid me, pray do so, and anyhow forgive me.

Yours very sincerely, CH. DARWIN.

MR. TORBITT'S EXPERIMENTS ON THE POTATO-DISEASE.

[Mr. James Torbitt, of Belfast, has been engaged for the last twelve years in the difficult undertaking, in which he has been to a large extent successful, of raising fungus-proof varieties of the potato. My father felt great interest in Mr. Torbitt's work, and corresponded with him from 1876 onwards. The following letter, giving a clear account of Mr. Torbitt's method and of my father's opinion of the probability of its success, was written with the idea that Government aid for the work might possibly be obtainable:]

CHARLES DARWIN TO T.H. FARRER.

Down, March 2, 1878.