Ontogeny of pollen wall ofleontodon autumnalis(hypochoeridinae, compositae)

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Abstract
Several development stages of 3-colpororate, echinolophate pollen grains of Leontodon autumnalis L. were studied with light microscope, scanning and transmission electron microscopes. The pattern of the tectum is differentiated in most respects in the early tetrad stages, and completed before digestion of the special callosic envelope. Differentiation of foot layer, columellae and endexine formed from material deposited on membranous lamellae during the free microspore stages. An increases in the volume of the protoplast apparently affected an extreme reduction of the foot layer in the regions of lacunae. The oral part of the colpororate aperture, was found to consist of two elliptical endexinous ora (os I and os II). Each os is covered by a membrane. These membranes developed by separation of lamellae at the margin of the oncus. The oral part of the aperture was seen to be covered by a plug.