A New Asexual Cycle in a Pediastrum simplex Strain

Abstract

In a freshly prepared soil-water medium, a Pediastrum simplex strain yielded a previously unreported asexual cycle. This cycle, requiring 2-5 days, began with motile cells released directly from azygotes Each motile cell developed into a flattened four-cornered polyeder The polyeder contents divided internally into four cells that remained together inside the polyeder cell wall to form a flat four-cornered colony After a short period of growth, the colony cells released motile cells directly into the culture medium Each motile cell developed into a flattened four-cornered azygote to complete the cycle The appearance of azygotes and polyeders of the fast cycle was identical After cultures aged for 6-8 mo, or when cultures were subjected to low temperatures, pH extremes, or contaminating algae, the fast-cycle cells were replaced by slow-cycle cells The latter, identical with an asexual cycle reported by Davis (1967) involving spherical four-spined azygotes produced by typical colony cells, required 1...