Capillitial Formation in Arcyria Cinerea

SUMMARY

The capillitial system in Arcyria cinerea originates from an anastomosing system of elongated vacuolar elements. This system forms very early in the development of the sporangium and assumes the position which will eventually be occupied by the capillitium. It appears that food vacuoles present in the precleavage sporangium are incorporated into the vacuolar system. Electron microscopic study reveals that the capillitial threads are formed by the deposition of a layer of material or wall just beneath the membrane separating the vacuolar system from the surrounding protoplasm. This material is apparently supplied by vesicles which fuse with the membrane and empty their contents into the vacuolar system. As the wall is formed, the material initially contained in the vacuole is trapped within the thread. A mature thread therefore consists of a central region filled with vacuolar material and an outer layer of fibrous material with high electron density. The entire capillitial system is completely formed by the time spore cleavage begins.