A Light and Electron Microscopic Study of Stalk Formation in the Myxomycete Arcyria Cinerea

SUMMARY

Stalk formation in Arcyria cinerea has been examined using both light and electron microscopy. The stalk of a mature sporangium consists of an outer wall or stalk tube which is filled with sporelike bodies. The stalk tube, which is composed of electron-dense, fibrillar material, is formed by a deposition of material by the protoplasm in the stalk region of the precleavage sporangium and by a condensation of the slime layer surrounding the lower portion of the young sporophore. As the stalk tube forms, the protoplasm filling the tube undergoes cleavage and forms small segments. Those in the upper portion of the stalk develop into what appear to be normal spores while the segments of protoplasm beneath them develop into sporelike bodies. These structures resemble normal spores in many respects, but they are much larger and characteristically multinucleate and highly vacuolate. In addition, the sporelike bodies are packed very closely together and are often fused with one another by their walls.