A light and electron microscopic study of sporulation in the myxomyceteStemonitis virginiensis

Summary The conversion of the plasmodium ofS. virginiensis into sporophores has been examined at both the light and electron microscopic levels. Particular attention has been paid to stalk and columella formation, capillitial formation, nuclear behavior during sporulation and spore formation. Both the stalk and columella are formed within the sporangial initial as intraprotoplasmic secretions. A portion of the capillitium arises directly from the columella while the remainder forms within an anastomosing system of tubular vacuoles. As spore cleavage begins the nuclei within the sporangium begin to divide mitotically. The protoplasmic content of the sporangium is first divided into small protospores which typically contain a single dividing nucleus. Following the completion of mitosis each of these segments cleaves into yet smaller segments which develop into spores. Meiosis occurs in the spores some 12–16 hours after cleavage.