REPRODUCTIVE CELLS. 



125 



one larger one in or near the centre. The cytoplasm becomes dis- 

 tributed round them in such a way as to lead to the presence of 

 three ceUs at each end, and the central definitive nucleus is usually 

 held in a central mass by " bridles " of protoplasm. Of the six 

 cellular structures present the three at the upper end constitute 

 the two synergidae (lying uppermost) and the egg-cell, the latter 

 of which is the effective female cell (also termed the oosphere). 



Fig. 94.— The Upper End of the Embryo-sac of Helleborus niger, 

 showing fusion of the "polar" nuclei. The two sjmergidse (s) and 

 the egg-oell (e) are also seen lying above the polar nuclei (from 

 a photomicrograph). 



whilst the three at the lower end are the antipodal cells. At 

 this stage the macrospore is completely matured and ready for 

 fertilisation. 



[Most of the preceding stages described may be seen in 

 Plate iii. and Pigs. 93 to 97 inclusive.] 



