Page:Collected Physical Papers.djvu/350

330 On the stoppage of light, the antagonistic A element ceases to be active, while D appears to be persistent.

The result is a sudden unmasking of the negative, hitherto held in balance during exposure to light. A negative response with subsequent recovery thus occurs on the cessation of light.

The responses of Musa and of actively assimilating Hydrilla are seen to exhibit characteristic differences on account of the relative predominance of the D- or A-effect. In Musa, D is predominant, A being exhibited either as a positive after-effect or by the overshooting of response in the positive direction. In an actively assimilating Hydrilla plant, on the other hand, A is predominant and the response is positive. In less vigorous Hydrilla the positive becomes masked by the negative, when the resultant response appears to be similar to that of Musa. (Life Movements in Plants, Vol. IV, 1923.)