ULTRASTRUCTURE, PROTOPLASMIC STREAMING, GROWTH AND TROPISMS OF PHYCOMYCES SPORANGIOPHORES

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Abstract
Summary: For a satisfactory explanation of the growth, protoplasmic streaming, and photo‐ and geo‐tropic responses of Phycomyces sporangiophores, information is needed concerning the ultrastructure of these coenocytic hyphae. The form and spatial distribution of vacuoles, and of the photoreceptors, are crucial to the analysis of phototropism. The ultrastructural basis of protoplasmic streaming and its bearing on the differential growth responses that produce tropisms need to be established, and so does a physical basis for geo‐perception. This paper describes the general ultrastructure of the growing zone of stage I and stage IVb sporangiophores viewed in transverse and longitudinal sections.Numerous small vacuoles are present in the upper part of the growth zone, and a large central vacuole extends to within I mm of the apex. The form and distribution of vesicles believed to he involved in wall growth, and of the nuclei and mitochondria, are described. Bundles of vesicles or coiled tubules of endoplasmic reticulum showing inter‐bundle spacing comparable to that of the separate strands of the multi‐striate streaming protoplasm are reported.

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