226 



MORPHOLOGY 



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); 509, beginning of sus- 

 pensor-formation (s), 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. 



