The Light-Sensitive System as the Basis of the Photic Responses of Phycomyces

Abstract

Sporangiophores of Phycomyces show 2 types of photic response: acceleration of the rate of elongation and phototropic bending. The total reaction time of each type of response consists of an exposure period, a "latent period," and an action time. The duration of the reaction time of each mode of response varies similarly as a function of the duration of exposure to light, for sufficiently brief exposures. The 2 responses are therefore based on the same photosensitive system. The velocity of the latent period process is directly proportional to the amount of preceding photochemical change.