Zygospore development inGilbertella persicaria(Eddy) Hesseltine was studied by light microscopy and by transmission and scanning electron microscopy. Cell walls of apically conjugating progametangia lose their separate identities in the fusion septum. Gametangial septa are formed, asynchronously to synchronously, on either side of the fusion septum by the centripetal coalescence of vesicles. Secondary thickening of these septa is more rapid and continues longer on the side towards the zygospore. The multilayered wall of the zygosporangium ultimately consists of outer and inner primary walls, a warted layer, and a smoothing or tertiary layer. Ahyaline quaternary layer with conical projections (zygospore wall) is formed within the zygosporangium. The observations obtained are correlated with existing ultrastructural information on zygosporogenesis in the Mucorales.
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