Whether a spore results from the sexual union of two similar gametes (zygospore) or from the fertilization of an egg-cell by the protoplasm of a male organ (oospore); or is developed asexually as a motile (zoospore) or a quiescent body cut off from a hypha (conidium) or developed along its course (oidium or chlamydospore), or in its protoplasm (endospore), are matters of importance which have their uses in the classification and terminology of spores, though in many respects they are largely of academic interest.
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 cytology of zygospore-formation is not known in detail; the so-called gametes which fuse are multinucleate and are no doubt of the nature of gametangia.
Ripe zygospore (b) between the suspensors (a).
Germinating zygospore with a germtube bearing a sporangium.
(1904); "Zygospore germination in the Mucorineae," Annales mycologici (1906).
When two similar zoogametes fuse, the process is conjugation, and the product a zygospore (Gr. ?"vy6, yoke).
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.
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.
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.
It would seem that in some cases the nuclei of the gametes remain distinct in the zygospore for a considerable time after conjugation.
In Zygnemaceae and Mesocarpaceae the zygospore, after a period of rest, germinates, to form a new filamentous colony; in Desmidiaceae its contents divide on germination, and thus give rise to two or more Desmids.