But it is difficult to apply such a term at all to those cases in which there intervene between the oospore and the next sexual stage a series of generations, the zoospores of which are all precisely similar.
Oogonium and development of the oospore in Peronospora.
There is here obviously a certain parallelism with the case of Bryophyta, where the sporogonium arising from the oospore is epiphytic and partially parasitic upon the female plant, and always culminates in the production of spores.
Among Chlorophyceae it is often the case that the oospore on germination divides up directly to form a brood of zoospores.
Not even Riccia, with its rudimentary sporogonium, has so simple a corresponding stage as Bangia, for, while there is some amount of sterile tissue in Riccia, in Bangia the oospore completely divides to form carpospores.
After fertilization the equivalent of the oospore divides directly to form a group of carpospores.
Among Phaeophyceae it is well known that the oospore of Fucaceae germinates directly into the sexual plant, and there is thus only one generation.
This peculiar product of germination, which intervenes between the oospore and the adult form, is the proembryo.
Excluding Bangiaceae, however, from consideration, the Euflorideae present in the product of the development of the oospore like Bryophyta a structure partly sterile and partly fertile.
The spores of the Aglaozonia form are known to give rise to sexual plants, and the oospore of Cutleria has been observed to grow into rudimentary Aglaozonia.