Notes And Study Material for Exam Papers

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 consistin...

An ovule (megasporangium) may arise from the placenta at the base of the ovary or on the inner surface of the ovary. It is borne on a distinct stalk, the funicle which is attached to the body of the ovule at a point called the hilum. The central and somewhat conical part of the ovule is the nucellus. It consists of a mass of parenchymatous cells. It represents the metasporangium proper and is invested by two-layered integuments in monocotyledons and primitive dicotyledons (Archicliamydeae) but by single-layered integument in the higher dicotyledonous families (metachlamydeae); very rarely unitegmic and bitegmic ovules occur in the same family. In many cases, single integument has resulted due to the fusion of two separate primordials or by elimination of one of the two integuments. The third integument in the form or aril is found in plants like Asphodehus and Trianthema, while Ricinus and several other plants of the family, Euphorbiaceae, show an integumentary proliferation calle...