Page:Life Movements in Plants.djvu/256

226 stimulus on tissues in which growth, on account of extreme sub-tonicity, has been brought to a state of standstill.

The modifying inﬂuence of tonic condition on reSponse is similar in pulvinated and growing organs.

The motile organ of Mimosa in a condition of sub-toni- city, exhibits a positim response, by expansion, increase of turgor. and erection of the. leaf. Continuous stimulation conVerts the abnormal positive to normal negative.

In suh-tonic growing organs stimulus likewise induces a post/um response, by expansion, increase of turgor and acceleration of the rate of growth. Continuous stimulation conVerts the abnormal acceleration to normal retardation.

Sub-minimal stimulus tends to induce even in normal tissues, an acceleration of rate of growth. Stimulus of moderate intensity induces in the same tissue the. normal retardation of growth.