Page:Life Movements in Plants.djvu/266

236 second vertically upwards, and the third ht‘orizontally for- ward from the side opposite. the. lantern. The effect of light is seen d.-monstratcd in Fig. Sti.

Fig. 86. — Effect of light on pulsation of Desmodium leaflet. Duration of application of light is represented by the horizontal line. Up-curve represents diastolic expansion and down-curve bystolic contraction. IJole contractile effect of light in diminution of amplitude and r duction of diastolic limi. of pulsation.

Light was applied at the second pulsation. It will be seen that light retards or arrests the autonomous activity. On the cessation of light the normal activity was found to be gradually restored. It is of much interest to note here the similarity of action of light on autonomous acti- vity of the leaflet of Desmodium and of a growing organ. In both, we find that while in the sub-tonic condition of the tissue the effect of light is to enhanc or renew the autonomous activity of growth and pulsation, in normal condition the effect is to retard it.

Inspection of the record exhibits another very interest- ing characteristic. We saw that light retarded growth by inducing an incipient contraction. In the Desmodium leaflet the contractile reaction of light is exhibited by the characteristic modification of its .pulsations. The duration