CHAPTER 5 

 THE MALE GAMETOPHYTE 1 



The development of the male gametophyte is remarkably uniform 

 in angiosperms. The microspore, which is the first cell of the 

 gametophyte generation, undergoes only two divisions. The first 

 division gives rise to a large vegetative cell and a small generative 

 cell (Fig. 95 A-F). The second, which concerns only the generative 

 cell, may take place either in the pollen grain (Fig. 95G-H) or in the 

 pollen tube (Fig. 95/-/) and gives rise to the two male gametes. 

 Details of the process may be considered under the following heads : 

 microspore, formation of the vegetative and generative cells, divi- 

 sion of the generative cell, male "cells" or "nuclei," and vegetative 

 nucleus. 



Microspore. The newly formed microspore has a very dense 

 cytoplasm with a centrally situated nucleus, but the cell rapidly 

 increases in volume and the accompanying vacuolation is followed 

 by a displacement of the nucleus from the center to a place adjacent 

 to the wall. In most tropical plants the nucleus begins to divide 

 almost immediately, but in plants belonging to colder regions 

 there is often a resting stage lasting from a few days to several weeks. 

 To mention a few instances, in Tradescantia reflexa the resting 

 period of the microspore is about four days or less, in Styrax obassia 

 about a week, and in Himantoglossum hircinum between two to three 

 weeks. In Uvularia sessilifolia, Empetrum nigrum, and Betula 

 odorata, the microspores are said to pass the entire winter in the 

 uninucleate stage (for further information, see Dahlgren, 1915; 

 Finn, 1937a). 



Formation of Vegetative and Generative Cells. The first division 

 of the microspore gives rise to the vegetative and generative cells. 

 Geitler (1935) noted that the metaphase spindle usually shows a 



1 For more detailed information on the development and organization of the male 

 gametophyte, see Wulff and Maheshwari (1938) and Maheshwari (1949). The 

 technique for the study of the male gametophyte has been reviewed in another 

 paper by Maheshwari and Wulff (1937). 



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