Page:Life Movements in Plants.djvu/245

stronger stimulus the response became diphasic, positive followed by negative. Direct stimulus induced a negative response.

Since the responsive. reactions of growing and non-growing organs are, as we shall find later. fundamentally similar, I expected that Indirect stimulus would give rise in a growing organ to an effect which would he of opposite sign to that induced by Direct stimulus—an acceleration, instead of retardation of growth; that would correspond to the positive mechanical and electrical responses to Indirect stimulus given by pulvinated organs and by ordinary vegetable tissues. The account of the following typical experiment will show that my anticipations have been fully verified.

Experiment 86.—I took a growing bud of Crinum and determined the region of its growth activity; lower down a region was found where the growth had attained its maximum and may, therefore, be regarded as indifferent region. I applied two electrodes in this indifferent region about 1 cm. below the region of growth. On application of moderate electric stimulus of short duration the response was by an acceleration of growth which persisted for nearly a minute, after which there was a resumption of the normal rate of growth. In this particular case the interval of time between the application of stimulus and the responsive acceleration of growth was 12 seconds. The interval varies in different cases from one second to 20 seconds or more, depending on the intervening distance between the point of application of stimulus and the