Page:Life Movements in Plants.djvu/237

Rh due. to the want of snllicieut delicate. means of obs-31":- tion. For my recorders indicate in some cases a response within less than 2 seconds of the incidence of light. This was found, for example, in the record of response given by a seedling of Curler/um, to a rlash of ultra-violet light. In the majority of cases the, response is observed within .15 seconds of the incidence of light.

Experiment 7.9.——F0r the determination of the. latent period, a record of the ell'ect of are light. of 30 seconds’ duration vas taken on a moving plate. It will he noticed (Fig. 76) othat a retardation of growth was induced

Fm. TIE.» Latent. period and Hum-relations of response to light, applied at. thick line. Successive dots at intervals of :3 st-t‘. within 35 seconds of the incidence of light. 'l‘he. in- cipient contraction induced by light is thus similar to that induced by any other form of stimulus. (lrowth became restored to the normal valu-, 5 minutes after the, cessation of Silllltllllx'.

Eajicrimeut 80.—-—I next studied the action of light, the intensity of which was increased in arithmetical