Microsporogenesis

Structure of the anther in orchids is very much the same as in other angiosperms. The sporogenous tissue is enclosed by the anther wall which is multilayered consisting of an epidermis , endothecium , two middle layers and a tapetum. The tapetum in Paphiopedilum drurii is binucleate , whereas in all the monadrous orchids it is uninucleate .

The archesporial cells undergo mitosis one to give rise to microspore mother cells. Meiotic division in these cells are simultaneous giving rise to four haploid cells , which in the majority of case remain together . The tetrads are mostly isobilateral , sometimes tetrahedral and in a very few cases T-shaped . In the whole of Diandrae and in a very few Monandrae as for eg. Vanilla ,Cephalanthera etc. individual cells round off investing themselves with a thick wall and behaving as pollen of other angiosperms. In Pogonia and Spiranthes the individual pollen grains adhere in tetrads forming compound pollen grains . In Peristylus , of the tribe Orchideae the pollen arising from one archesporial cell remain together to form ;massulae’ . In still advanced forms, the tetrads adhere together with varying degrees of firmness to form pollinia .

The nucleus divides unequally into a larger vegetative and a smaller generative nucleus . The generative nucleus usually lies closer to the periphery of the pollen cell. An incipient wall is formed in between these two nuclei, which later disintegrates. Possibly due to the pressure exerted by the vegetative cell, the generative cell assumes the shape of a crescent . Eventually this cell is engulfed by the cytoplasm the shape of a crescent . Eventually this cell is engulfed by the cytoplasm of the vegetative cell . In this condition the pollen is ready to be transported to the stigmatic surface.