Some general observations on zoospores of the chytrid Rhizophydium planktonicum Canter emend

General microscopic observations of zoospores of the chytrid Rhizophydium planktonicum Canter emend., contained within a small glass chamber, have shown that they have strong reactions to visible light. There appears to exist a threshold level of dim light below which zoospores will eventually enter what is termed the 'state of quiescence' and above which they will continue to maintain active swimming. Alternations between these two states can be manipulated with ease under the microscope. Free swimming zoospores after a period in dim light or darkness and quiescent zoospores both respond to sudden exposure to bright light. The concentration of zoospores into aggregates of individuals circling at the upper and or lower surfaces of a chamber is recorded. As viewed from above, those uppermost circle in a clockwise direction while those below go round counter-clockwise. Adherence between zoospores as swimming individuals or in the encysted state has been seen but there is no evidence of any fusion taking place. A specially adapted channel image intensifier made possible the examination of material under infra-red.