Mr. Thiselton Dyer ('Charles Darwin' ('Nature' Series), page 41.) has well said: "Whether this masterly conception of the unity of what has hitherto seemed a chaos of unrelated phenomena will be sustained, time alone will show. But no one can doubt the importance of what Mr. Darwin has done, in showing that for the future the phenomena of plant movement can and indeed must be studied from a single point of view."
The work was begun in the summer of 1877, after the publication of 'Different Forms of Flowers,' and by the autumn his enthusiasm for the subject was thoroughly established, and he wrote to Mr. Dyer: "I am all on fire at the work." At this time he was studying the movements of cotyledons, in which the sleep of plants is to be observed in its simplest form; in the following spring he was trying to discover what useful purpose these sleep-movements could serve, and wrote to Sir Joseph Hooker (March 25th, 1878):—
"I think we have PROVED that the sleep of plants is to lessen the injury to the leaves from radiation. This has interested me much, and has cost us great labour, as it has been a problem since the time of Linnaeus. But we have killed or badly injured a multitude of plants: N.B.—Oxalis carnosa was most valuable, but last night was killed."
His letters of this period do not give any connected account of the progress of the work. The two following are given as being characteristic of the author:]
CHARLES DARWIN TO W. THISELTON DYER. Down, June 2, 1878.
My dear Dyer,
I remember saying that I should die a disgraced man if I did not observe a seedling Cactus and Cycas, and you have saved me from this horrible fate, as they move splendidly and normally. But I have two questions to ask: the Cycas observed was a huge seed in a broad and very shallow pot with cocoa-nut fibre as I suppose. It was named only Cycas. Was it Cycas pectinata? I suppose that I cannot be wrong in believing that what first appears above ground is a true leaf, for I can see no stem or axis. Lastly, you may remember that I said that we could not raise Opuntia nigricans; now I must confess to a piece of stupidity; one did come up, but my gardener and self stared at it, and concluded that it could not be a seedling Opuntia, but now that I have seen one of O. basilaris, I am sure it was; I observed it only casually, and saw movements, which makes me wish to observe carefully another. If you have any fruit, will Mr. Lynch (Mr. R.I. Lynch, now Curator of the Botanic Garden at Cambridge was at this time in the Royal Gardens, Kew.) be so kind as to send one more?
I am working away like a slave at radicles [roots] and at movements of true leaves, for I have pretty well done with cotyledons...
That was an EXCELLENT letter about the Gardens (This refers to an attempt to induce the Government to open the Royal Gardens at Kew in the morning.): I had hoped that the agitation was over. Politicians are a poor truckling lot, for [they] must see the wretched effects of keeping the gardens open all day long.
Your ever troublesome friend, CH. DARWIN.