226 



MctKl'HOLOGY 



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502 



503 • 



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505 



Figs. 502-509. — Development of embryo of Pinus: 502, fusion of male and female 

 nuclei in the large egg; 503, four free nuclei (one in background) derived from fusion 

 nucleus; 504, the four nuclei (two visible) at base of egg and dividing; 505, eight- 

 nucleate stage (four nuclei visible); 506, the same a little further advanced; 507, next 

 division, resulting in twelve cells in three tiers; 508, completed proembryo (four tiers of 

 cells, uppermost open towards the general cytoplasm of the egg); 50c;, beginning of sus- 

 pensor-formation (.?), leaving within the egg the rosette cells (r), and thrusting out of it 

 the four tip cells, which will form the embryo. — After Coulter and Chamberlain. 



