On this basis, with other interesting morphological comparisons, Brefeld erected his hypothesis, now untenable, that the Ascomycetes and Basidiomycetes diverge from the Zygomycetes, the former having particularly specialized the ascus (sporangial) mode of reproduction, the latter having specialized the conidial (indehiscent one-spored sporangiole) mode.
At the time of sporangial formation the protoplasm with numerous nuclei streams into the swollen end of the sporangiophore and there becomes cut off by a cell-wall to form the sporangium.
The escape of zoospores is effected by the degeneration of the sporangial wall (Chaetophora), or by a pore (Cladophora), a slit (Pediastrum), or a circular fracture (Oedogonium).
The sporangial wall, consisting of several layers of cells, encloses a cavity containing numerous oval spores (pollen-grains).
The tapetal layer is partly formed from the sporangial wall and partly as a layer covering the trabeculae.
The spores, which are set free by the rotting of the sporangial wall, germinate much as in the case of Selaginella, though the similarity may be a case of independent resemblance.
It is thus proved that the sporangiophore is not a mere sporangial stalk, but a distinct organ, in all probability representing a ventral lobe of the subtending bract.
The synangia consist of a stout wall composed of thick-walled cells, succeeded by a layer of more delicate and smaller elements; and internal to the wall occur two rows of sporangial loculi containing microspores.
9, Synangium, in transverse section, showing sporangial groups, m, and microspores, 1.