Zur vergleichenden Morphologie der CyanophyceeClastidium setigerum und verwandter Gattungen

InClastidium setigerum the mature plant consists of the contents of the endosporangium, the sporangium itself is represented only by a basal cup-shaped cell wall. This cup-shaped wall originates, while the sporangium contents grow out during a very juvenile stage. The spores are homologous to the endospores of related genera but they are not “endo” spores in the literal sense, because they are never surrounded by a common wall. Sporogenesis occurs belated, that is only after the emergence of the sporangium contents, and is effected by centripetally growing-in of the delicate special wall (Eigenwand) of the sporangium contents.Clastidium therefore represents a very remarkable derived member ofDermocarpaceae, but also shows close relationship toCyanophanon. In this connection the systematic position ofGeitleribactron is thoroughly discussed: The morphological peculiarities of this genus, newly created as aChroococcacea byKomárek, are better understood, if the genus is considered as an extremely derived member ofDermocarpaceae with total suppression of a sporangium in the strict sense.