Ultrastructure of the Resin Ducts of Mangifera indica L. (Anacardiaceae). 1. Differentiation and Senescence of the Shoot Ducts

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Abstract
A detailed electron microscope study has led to the conclusion that the resin ducts of the shoot of Mangifera indica L. develop lysigenously. This study has also established several characteristics which can serve as criteria for a clear distinction between schizogenous and lysigenous cavities. The main characteristics of lysigenous cavities are: (1) The presence of disorganized cytoplasm in the duct cavity. (2) The presence of wall remains attached to the wall of living epithelial cells facing the cavity. (3) The presence of specific intercellular spaces at the cell corners facing the duct lumen. Duct development starts with the disintegration of a file of cells forming an initial cavity. Later the cells lining this cavity differentiate into cells secreting lipophilic compounds. As a result of growth and differentiation of the tissues around the duct, its lumen becomes compressed and comes to resemble a branched narrow slit. Such a slit may wrongly be regarded as an initial stage of a schizogenous duct. Disintegration of epithelial cells occurs throughout all stages of development. Neighbouring cells partly fill the space which is released by disintegrating cells. At the end of the stage of secretion the cytoplasm of all epithelial cells darkens, preceding their disintegration. This darkening is a gradual process which begins in the vicinity of ribosomes. When all dark epithelial cells disintegrate the cavity widens and the neighbouring parenchyma cells substitute for the secretory epithelium without undergoing any significant change in their cytoplasm.

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