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LIFE MOVEMENTS IN PLANTS

effective in exciting the sensitive Mimosa and in retarding the rate of growth.


Fig. 92.—Effect of infra-red rays on the pulvinus of Mimosa.

DIVERSE MODES OF RESPONSE TO STIMULUS.

In Mimosa excitation is followed by the striking manifestation of the fall of the leaf. But in rigid trees contraction under excitation cannot find expression in movements. I have shown elsewhere that even in the absence of realised movement, the state of excitation can be detected by the induced electro-motive change. I have shown that not only every plant but every organ of every plant is sensitive and reacts to stimulus by electric response of galvanometric negativity.[1]

There is an additional electric method by which the excitatory change may be recorded. I find that excitation induces a variation of the electrical resistance of a vegetable tissue.[2] Thus the same excitatory reaction finds

  1. ↑ Bose—Friday Evening Discourse—Royal Institution of Great Britain, May 1901.
  2. ↑ This variation is sometimes positive, and at other times negative, according to the condition of the tissue.
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