GROWTH AND MATING OF GONIUM PECTORALE (VOLVOCALES) IN DEFINED MEDIA(1).

Growth in defined media of 32 populations of Gonium pectorale was studied to learn more about the sexual isolation reported for this species. The 23 populations containing both mating types (+ & -) icere also studied for the ability to form zygotes in defined media. A preliminary study showed that some populations grew and reproduced sexually in a defined mineral medium, whereas others appeared to require exogenous organic materials for growth and/or zygote formation. The diverse reactions exhibited by the populations indicate physiological races which may explain, in part, the occurrence of sexual isolation.