Electron‐Microscopic Demonstration of Plastids in Polytoma*

SYNOPSIS. The subcortical network identified as a leucoplast in Polytoma by some light microscopists actually consists of a system of branching mitochondria. A starch‐bearing plastid which may also contain stigma granules occurs beneath the mitochondrial layer. Tubular profiles in the plastid similar to those seen in a Chlamydomonas mutant may be significant to the hypothesis of the origin of Polytoma from a Chlamydomonas‐like organism by step‐wise loss of chlorophyll‐synthesizing ability. The basal bodies of the two typical flagella are connected by an additional broad fibril which arches across the anterior papilla.