[Ultrastructure of the leaf cells of young and old branches of Mnium and its relation to ion uptake].

Differences in the ultrastructure of the leaf cells of young and old branches of Mnium are demonstrated. The appearance of the cytoplasm and the endoplasmatic reticulum membranes differs with the age of the leaves. In the young leaves numerous vesicles are found within the tonoplast. Quite pronounced are changes in plastid structure. Compared with those of the young leaves the chloroplasts of the old leaf cells have many more thylacoid membranes which form large grana. The changes in ultrastructure coincide with differences in transport phenomena reported earlier. A few speculations on the possible significance of this correlation are presented.