Sexuality in Physoderma Pulposum Wallroth

SUMMARY

In mixtures of planospores derived from two or more epibiotic sporangia of Physoderma pulposum, several planospores function as gametes, pair, and fuse to form zygotes. Planospores from single epibioti sporangia, or from germinating resting sporangia, however, do not copulate but infect the host as zoospores and give rise to epibiotic sporangia. The gametes form pairs, clumps, or long chains. After continuing together for more than 1 hour the pairs may separate, or ultimately settle down and fuse. In the later case, one of the gametes of the pair becomes sluggish and settles down, whereas the other gamete remains active for some time more. When both are quiescent, they develop pseudopodia and fuse. The resulting zygotes are feebly motile, and they may be uni- or biflagellate depending on whether or not the flagellum of on of the gametes was absorbed before plasmogamy. After a brief period of motility the zygote settles down and absorbs the flagellum. Karyogamy occurs at this stage.