Electron microscope observations on the differentiation of protocorm cells of Dactylorhiza maculata

The fine structure of aseptically cultivated protocorm cells of Dactylorhiza maculata (L.) Sod was studied with special reference to differentiation of leaf cells. In the young protocorm the characteristic structures are compound amyloplasts and smooth ER. In the older, the green shoot pole contains many proplastids storing starch, some membrane–bound protein crystalloids and lipid droplets attached to the nuclear membrane and plasmalemma. In the leaves of the young seedling, two types of chloroplasts are found. One contains little or no starch but many osmiophilic plasto–globuli; the other has only a few plastoglobuli but a large starch grain.