DEVELOPMENT AND STRUCTURE OF PHLOEM IN THE PETIOLE OF LUFFA CYLINDRICA

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Abstract
Differentiation of external phloem is earlier than that of internal phloem in the young petiole of Luffa cylindrical. For a single sieve‐tube element, one to six companion cells are present. The young sieve element shows many globular slime bodies which fuse longitudinally and disperse into the cytoplasm. Simultaneously the nucleus loses its stainable contents and later disorganizes. The contents of the sieve element are in the form of plugs, strands or a granular mass. Undispersed slime in the form of discrete bodies along the lateral walls is also observed. During one stage, at least, the dispersed slime and other contents of a mature sieve element lie at the periphery around a central cavity. A special type of phloem‐parenchyma cell shows disorganizing chloroplasts, an extruded nucleolus, and callose on primary pit fields.