Development of pollinium in two epidendroid orchids.

摘要

Development of pollinium has been studied in Cymbidium aloifolium (tribe Cymbidieae) and Smitinandia micrantha (tribe Vandeae) of the family Orchidaceae. The anther primordium develops two lobes oriented towards the labellum. Each lobe has a group of archesporial cells, which divide mitotically so as to form a spherical mass of sporogenous cells, in which there is differentiation of a dorsiventral plate of elongated sterile cells. In C. aloifolium, the sterile plate extends into about three-fourths of the fertile tissue, whereas in S. micrantha it is complete but asymmetrically oriented. Synchronous meiosis in the microsporocytes is followed by simultaneous cytokinesis so as to form microspore tetrads which organize into pollinia. Centripetal disintegration of the sterile plate during development of the male gametophyte forms two perforate (hollow) pollinia in C. aloifolium, but four unequal pollinia in S. micrantha. The anther wall is composed of an epidermis, an endothecium, two to three middle layers and the tapetum. The tapetum disorganizes during development of the male gametophyte, while the endothecium and adjacent middle layers develop fibrous thickenings..