MOVEMENT IN PLANTS.
“The Power of Movements in Plants” was published on November 6th, 1880. It embodies a vast amount of work carried on in conjunction with Francis Darwin. This volume bears a very direct relation to that last mentioned, as Darwin has explained in his Autobiography:—
“In accordance with the principle of evolution it was impossible to account for climbing plants having been developed in so many widely different groups unless all kinds of plants possess some slight power of movement of an analogous kind. This I proved to be the case; and I was further led to a rather wide generalisation, viz. that the great and important classes of movements, excited by light, the attraction of gravity, &c., are all modified forms of the fundamental movement of circumnutation.”
An extreme example of circumnutation has already been described in the revolving movements of the youngest parts of the stem of a twining plant.
The work evoked very great interest in this country, but was severely criticised by certain German botanists. The immense number of new observations must always have a very high value, whatever be the fate of the general conclusions, concerning which it may be remarked that Darwin’s conclusions have often been criticised before, but time has shown that he was right.
“Insectivorous Plants” was published July 2nd, 1875, but I consider it last, as the subject stands somewhat apart from the rest of his botanical works. The subject was suggested to him by noticing the insects caught by the leaves of the Sun-dew (Drosera) near Hartfield. He then studied in great detail the causes of the movement, and the sensitiveness of the gland-tipped hairs, finding that a piece of hair weighing 1/78000 of a grain causes one of them to curve inwards, and alters “the condition of the contents of every cell in the foot-stalk of the gland.”
The greater part of the work deals with the experiments on Drosera, which were extremely numerous and detailed. The remainder treats of other insectivorous plants, such as Dionæa, Pinguicula, Utricularia, etc. The methods of capture, the movements of the plants under the stimulus supplied by the living insect (or other animal), and the resulting changes in the plant-cells were not the only points studied. He also investigated the digestive secretion and its action upon the food absorbed by the leaves.
CHAPTER XXV.
LETTERS FROM DARWIN TO PROFESSOR MELDOLA (1871–82).
By the kindness of my friend Professor Meldola, and the courtesy of Mr. Francis Darwin, I am enabled to publish for the first time a series of letters written by Charles Darwin to the former. The whole series consists of 33 letters, written between January 28th, 1871, and February 2nd, 1882, only a few weeks before his death.