The zygospore becomes surrounded with its own wall, consisting finally of three layers, the outer of which is furnished with spicular prominences of various forms. In Zygnemaceae there is no dissolution of the filaments, but the whole contents of one cell pass over by means of a conjugation-tube into the cavity of a cell of a neighbouring filament, where the zygospore is formed by the fusion of the two FIG.
Solenia, Cyphella - and even simpler cases are met with in Mortierella, where the zygospore is invested by the overgrowth of a dense mat of closely branching hyphae, and in Gymnoascus, where a loose mat of similarly barren hyphae covers in the tufts of asci as they develop.
The germination of a zygospore or oospore is effected by the rupture of an outer cuticularized exosporium; then the cell may protrude an inner wall, the endosporium, and grow out into the new plant (Vaucheria), or the contents may break up into a first brood of zoospores.
It would seem that in some cases the nuclei of the gametes remain distinct in the zygospore for a considerable time after conjugation.
Germinating zygospore with a germtube bearing a sporangium.
Some Zygnemaceae and Mesocarpaceae form either a short conjugating tube, or none at all, but the filaments approach each other by a knee-like bend, and the zygospore is formed at the point of contact, often being partially contained within the walls of the parent-cell.