180 EVOLUTION OF PLANTS 



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(Fig. 44, B, pri) coalesce. About the three nuclei at 

 the upper or micropylar end of the embryo-sac there is 

 formed an aggregation of protoplasm resulting in three 

 naked cells, which constitute the so-called " egg-appa- 

 ratus." The three nuclei at the other end become also 

 surrounded by protoplasm, which usually is bounded 

 by a definite cell-wall. These three cells are called the 

 antipodal cells (Fig. 44, B, ant). 



In some of the simpler Monocotyledons, e.g. the 

 grasses, the number of antipodal cells is more numer- 

 ous, and a few cases are known where there seems to 

 be a multiplication of the other cells within the embryo- 

 sac ; but these are not yet sufficiently understood to 

 throw much light upon the homologies existing between 

 the female gametophyte of the Angiosperms and that 

 of the Gymnosperms and heterosporous Pteridophytes. 

 Whether the egg-apparatus is to be considered as a 

 single archegonium, or whether each of its cells is to 

 be so regarded, cannot be positively decided at present. 

 The other cells, i.e. the antipodals and the endosperm 

 cells formed later, represent probably the vegetative 

 part of the gametophyte. 



The microsporangia are much less modified, and the 

 development of the microspores (pollen) corresponds 

 exactly with that of the Gymnosperms and the Arche- 

 goniates from the mosses up, even to the final division 

 of the mother-cell into four spores. The ripe pollen- 

 spore shows exactly the same structure as the spores 

 of the Archegoniates. On germination two cells are 

 formed, a large vegetative one and a small antheridial 

 cell (Fig. 44, C). The former, when the spore falls 

 upon the pistil, develops into the pollen-tube, and the 



