Microsporangium and The Male Gametophyte

Usually anther is bithecous with 4 microsporangia. Occasionally one or more microsporangium may be suppressed. The development of microsporangium and male gametophyte was studied by Kanta (1962). The fertile microsporangium has 46 layers of compactly arranged microspore mother cells. No wall is laid down between the daughter nuclei after the first reduction division. Wall formation occurs

Figure 2.17 Development of megasporangium and female gametophyte. 1. L.S. of nucellus with a hypodermal archesporial cell. 2. Multicelled archisporium; 3. Megaspore mother cell with primary parietal cell. 4. Periclinal division of the parietal cell; 5. L.S. of ovule with a megaspore mother cell and three parietal layers; 6. Megaspore mother cell; 7. Two nucleate embryosac; 8-9, primary 4—nucleate embryosac; 10-11. Megaspore showing 1+3 arrangements of nuclei; 12. Same with nuclei at metaphase; 13. Secondary 4 nucleate embryosac; 14. A mature embryosac; 15. Micropylar portion of a mature embryosac showing egg apparatus and secondary nucleus (Allx1184) e—egg; s—synergid; ant—antipodals; scn—secondary nucleus. (After Kanta 1962).

Figure 2.17 Development of megasporangium and female gametophyte. 1. L.S. of nucellus with a hypodermal archesporial cell. 2. Multicelled archisporium; 3. Megaspore mother cell with primary parietal cell. 4. Periclinal division of the parietal cell; 5. L.S. of ovule with a megaspore mother cell and three parietal layers; 6. Megaspore mother cell; 7. Two nucleate embryosac; 8-9, primary 4—nucleate embryosac; 10-11. Megaspore showing 1+3 arrangements of nuclei; 12. Same with nuclei at metaphase; 13. Secondary 4 nucleate embryosac; 14. A mature embryosac; 15. Micropylar portion of a mature embryosac showing egg apparatus and secondary nucleus (Allx1184) e—egg; s—synergid; ant—antipodals; scn—secondary nucleus. (After Kanta 1962).

after meiosis II resulting in tetrahedral or occasionally in bilateral tetrads. On separation the microspore become more or less spherical. The nucleus divides into a large round vegetative nucleus and a small spindle shaped generative nucleus, separated by a wall. The mature pollen grains have smooth exine.

The anther wall consists of the epidermis, endothecium, 2-3 middle layers and the tapetum. The tapetal cells often become binucleate. The endothecium develops thickenings at the tangential walls. As the anther matures, the tapetal cells lose contact with one another and finally disintegrate. Thus the mature anther wall consists only of epidermis and the fibrous endothecium. The anther dehisces by an apical slit.

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