Describe structure and development of Anther and Microsporangia



A cross section of young anther shows that each anther lobe contains two pollen sacs or microsporangia but the number may vary among different angiosperms from one to many. As a rule microsporangia extend as longitudinally running sacs through the entire length of the anther. Later on as the anther matures, the intervening tissue breaks down between each pair of pollen sacs and the two pollen sacs coalense into one, thus forming two large cavities instead of four in each anther. In Malvaceae anthers are one called (monotherous) as there are two instead of four pollen sacs per anther and these also coalesce at maturity to form single loculus. Very rarely four celled sacs may remain separate in a mature anther.

Within each pollen sac of an angiosperm as within a Microsporangium of Salaginella or Pinus are produced small numbers of micropyle mother cells surrounded by a conspicuous layer of nutritive cells, the tapetum outside the tapetum is the wall of the sporangium consisting of a number of layers of cells. Outermost wall layer just beneath the epidermis shows characteristic band-like fibrous thickenings. This layer is the endothecium which assists mechanically in the dehiscence of the anther opposite the partition between each pair of sporangia (pollen sacs) the cells of endothecium are thin walled and constitute the stomium which marks the line of dehiscence or opening of ripe anther. Each microspore mother cell after two successive divisions of its nucleus divides to produce four pollen grains (microspores). As this occurs and as the pollen grains mature, the tapetum disappears, the products of its disintegration are absorbed and used as food by the developing pollen grains.

Pollen grains are liberated as a result of dehiscence of ripe anther which may take place in various ways. In tulips, lily and Datura the opening is longitudinal e.g. the slit appears above the line of fusion of two pollen sacs; in others as barberry, it is effected by uplifting valves; in still others by means of pores at the top as in tomato, potato and certain other grasses by transverse slits in Hibiscus esculentus.

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