Page:Life Movements in Plants.djvu/257



The autonomous activrty of growth is ultimately derived from enlrgy supplied by the ciu'ironment. The internal activity may fall below par with consequent. diminution or even arrest of growth; this condition of the tissue 1 have designated as suh-tonic. The inert. plant. can only he stirred up to a state of activity hy stimulus from outside; and we saw that under the action of stimulus the rate of growth of a suh-tonic tissue was enhanced.

As the general quesdon of .leprcssion of autonomous acti- vity and its restoration hy the action of stimulus is of much theoretical importanve, I shall descrin experinn-nts carried out on a ditl'ercnt form of autonomous activity, seen in spontaneous pulsation ot' the lati-ral loath-ts ot‘ [hiwmdimn gyrans'. Under favourable conditions of light, and warmth these. leatlets «um-cuti- vigorous movements, the period of a singli- pulse varyingr from one to two minutes. As the energy for this activity is ultimately derived from the environment, it. is clear that isolation from the action of favourahlv environment will bring about a gradual depletion of energy with concomitant decline and ultimate Cessation of Spontaneous movement. For this we may keep the plant in semi-darl<ne~'s; we may further hasten the rundown process by isolating the leaﬂet. from the parent plant. A leaflet immersed in water was kept in a dimly lighted room; it was attached by a