Page:Life Movements in Plants.djvu/250

220 particular specimen which exhibited the abnormal positive I'eSpOl’lSG had a much feehler rate of growth of .0'30 a per second. As activity of growth in a plant is an index of its health)’ tone, a feeble rate of growth must be indicative of tonicity below par. The fact that plants in suh-touie condition exhibit abnormal acceleration of growth under stimulus will be seen further demonstrated in the next experiment.

In the parallel phenomenon of the response of pul- vinated organs we found that under condition of sub- tonicity, the response becomes positive and that' this ahuor- mal positive is converted into normal negative in com sequence of repeated stimulation. In growth, response likewise the. annornal acceleration of growth under light in the suh-tonie specimen of [Cg/Sour was conVerted into normal retardation after continuous stimulation for half an hour. From the facts given above, we are justiﬁed in drawing the following conclusions:

(I) That while light inducus a retardation of growth in a tissue whose tonic condition is normal or above. par, it brings about an (u-«w/m'u/ion in a tissue whose condi- tion is below par.

(2) That by the action of the. stimulus of light itself a suh~tonic tissie is raised to a condition at par, with the. concomitant restoration of normal mode of response by I'3tartlation of growth.

Another important question arises in this connection: Is the. restoration of normal response due to light as a form of stimulus, or to its photo-synthetic action? An answer to this is to be found from the results of an inquiry, whether a very diti'erent form of stimulus which exerts no photo-synthetic action, such as tentanising electric shocks, also induces a similar acceleration of growth in a sub-tonic tissue.