Abstract
Doses of ? rays up to 500 kr have no effect on the transformation of the regularly arranged tubuli of prolamellar bodies into clusters of vesicles, when after irradiation the plants are exposed to light. In the same way they do not prevent the de novo formation of prolamellar bodies when after the exposure to light, before or after irradiation, the plants are returned to darkness. Gamma rays (doses from 10-200 kr) however do considerably delay or even inhibit (500 kr) the development of grana and the simultaneous chlorophyll synthesis.