Page:Life Movements in Plants.djvu/270

240 4. The opposite effects of Direct and Indirect stimu- lus, both in motile and in growing organs.

5. The exhibition by all plant-organs of negative elec- tric response under Direct, and positive electric response under Indirect stimulus.

6. Similar modification of autonomous activity in Desmodium gyrans and in growing organs under parallel conditions.

7. Similar excitatory effects of various stimuli on pul- vinated and growing organs.

8. Similar discriminative effects of different rays of light in excitation of motile and growing organs.

I have shown (page I'JcS) 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 sti- mulus till growth becomes arrested. Above this critical intensity the inrluced contraction causes an actual shortening of the organ. There is no breach of continuity in the in- creasing contractile reaction, which at various stages appears as a retardation, an arrest of growth or a marked shorten- ing of length of the organ.

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