Page:Collected Physical Papers.djvu/349

Rh sativa in which chlorophyll is present in great abundance.

The fact that positive response is associated with assimilation is proved by my experiments on photo-electric response of water plants. This building up process by photosynthesis is here independently demonstrated by profuse evolution of oxygen. These aquatic plants exhibit marked positive electric response during strong illumination, recovery taking place on the cessation of light (fig. 101).

The positive element in the response may be indirectly demonstrated even in the normal Musa leaf. In figure 102 is seen the effect of continuous action of light which at first exhibits the predominant negative attaining a maximum; the positive element now begins to increase with the duration of light and causes a reversal; at a certain stage, the two elements, D and A, balance each other, the resulting response becoming horizontal.