Page:Insectivorous Plants, Darwin, 1899.djvu/76

CHAPTER IV.

THE EFFECTS OF HEAT ON THE LEAVES.

Nature of the experiments—Effects of boiling water―Warm water causes rapid inflection—Water at a higher temperature does not cause immediate inflection, but does not kill the leaves, as shown by their subsequent re-expansion and by the aggregation of the protoplasm—A still higher temperature kills the leaves and coagulates the albuminous contents of the glands.

In my observations on Drosera rotundifolia, the leaves seemed to be more quickly inflected over animal substances and to remain inflected for a longer period during very warm than during cold weather. I wished, therefore, to ascertain whether heat alone would induce inflection, and what temperature was the most eflScient. Another interesting point presented itself, namely, at what degree life was extinguished; for Drosera offers unusual facilities in this respect, not in the loss of the power of inflection, but in that of subsequent re-expansion, and more especially in the failure of the protoplasm to become aggregated, when the leaves after

being heated are immersed in a solution of carbonate of ammonia.^[1]

1. When my experiments on the effects of heat were made. I was not aware that the subject had been carefully investigated by several observers. For instance, Sachs Is convinced ('Traité de Botanique,' 1874. pp. 772. 854) that the most different kinds of plants all perish if kept for 10 m. in water at 43° to 46° Cent., or 113° to 115° Fahr.; and he concludes that the protoplasm within their cells always coagulates, if in a damp condition, at a temperature or between 50° and 60° Cent., or 122° to 140° Fahr. Max Schultze and Kühne (as quoted by Dr. Bastian in 'Contemp. Review,' 1874. p. 528) "found that the protoplasm of plant-cells, with which they experimented, was always killed and altered by a very brief exposure to a temperature of 118° Fahr. as a maximum." As my results are deduced from special phenomena, namely, the subsequent aggregation of the protoplasm and the re-expansion of the tentacles, they seem to me worth giving. We shall find that Drosera resists heat somewhat better than most other plants. That there should be considerable differences in this respect is not surprising, considering that some low vegetable organisms grow in hot springs-cases of which have been collected by Professor Wyman ('American Journal of Science.' vol. xllv. 1867). Thus. Dr. Hooker found Confervae in water at 168° Fahr.; Humboldt. at 185° Fahr.; and Descloizeaux, at 208° Fahr.