SEXUAL REPRODUCTION OF PERIDINUM CINCTUM F. OVOPLANUM (DINOPHYCEAE)1,2

Sexual reproduction is induced in the dinoflagelate Peridinium cinctum f. ovoplanum Lindemann when exponentially growing cells are inoculated into nitrogen deficient medium. Small, naked vegetative cells, produced by division of the thecate cells, then act as gametes. The zygote remains motile for 12–13 days during which time it enlarges and the theca which it forms becomes warty. Thirteen to 14 day s following plasmogamy the zygote is nonmotile, the protoplast contracts, a large red oil droplet appears, the wall thickens and becomes chitinized. This hypnozygote germinates within 7–8 weeks at 20 c producing 1 post-zygotic cell retaining the large red oil droplet. The presence of 4 nuclei in these post-zygotic cells may be demonstrated by staining them with acetocarmine. Two of these nuclei are smaller than the other two and probably abort. One may infer that meiosis occurs immediately prior to or at the germinartion of the hypnozygote. This post-zygotic cell divides within 24 h into 2 daughter cells each with a promment red oil droplet. These daughter cells divide after 2–3 days into ordinary vegetative cells. Attempts to induce sexual reproduction by changes in temperature or light and by inoculation of cells into media deficient in a number of basic elements were unsuccessful.