Development and ejection of ascospores from perithecia of Calonectria crotalariae occurred between 20-30 C with an optimum at ca. 25 C.  Ascospore ejection was stimulated by a reduction in relative humidity, but was not affected by raising the humidity.  Perithecia were capable of a second discharge 4-6 hours after being exhausted of mature ascospores.  Forcibly ejected ascospores were highly sensitive to desiccation.  Perithecial ontogeny and ascospore discharge mechanisms are described.

Additional key words: Arachis hypogaea, Cylindrocladium crotalariae, Cylindrocladium black rot.