OBSERVATIONS ON THE ORIGIN AND MULTIPLICATION OF PLASTIDS

Plastids were investigated in ultrathin sections of young developing tissues of corn endosperms, pea cotyledons, and potato. The electron photographs give support to the possibility that plastids are produced de novo, as well as by division. Some of the pictures suggest that, under certain conditions, plastids may also multiply by a process of delimitation brought about by invaginations of the plastid membrane.Several aspects of plastids and mitochondria can be directly compared, but the latter are much more limited in their response to environmental changes. An origin de novo for plastids is in agreement with known genetical behavior and results of recent biochemical investigations.