Page:Life Movements in Plants.djvu/245

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

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

Iaymriment 86.—-I took a growing hud of (lrinmn and determined the region of its growth activity; loWor down a region 'as found where the growth had attained its maximum and may, therefore. lie-regarded. as indill'orent region. I applied two electrodes in this inditl'erent region about. 1 cm. below tho 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 tho inter- val of time between the. application of stimulus and tho 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