Page:Life Movements in Plants.djvu/270

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LIFE MOVEMENTS IN PLANTS
  1. The opposite effects of Direct and Indirect stimulus, both in motile and in growing organs.
  2. The exhibition by all plant-organs of negative electric response under Direct, and positive electric response under Indirect stimulus.
  3. Similar modification of autonomous activity in Desmodium gyrans and in growing organs under parallel conditions.
  4. Similar excitatory effects of various stimuli on pulvinated and growing organs.
  5. Similar discriminative effects of different rays of light in excitation of motile and growing organs.

CONTRACTILE RESPONSE OF GROWING AND NON-GROWING ORGANS.

I have shown (page 198) that a growing organ under stimulus, undergoes an incipient contraction as shown in the responsive retardation of its rate of growth; that this retardation increases with the intensity of the incident stimulus till growth becomes arrested. Above this critical intensity the induced contraction causes an actual shortening of the organ. There is no breach of continuity in the increasing contractile reaction, which at various stages appears as a retardation, an arrest of growth or a marked shortening of length of the organ.

CONTRACTILE RESPONSE OF PULVINATED AND GROWING ORGANS.

Experiment 94.—In order to show the striking similarity between the response of 'sensitive' Mimosa and that of a

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