688 



A TEXTBOOK OF THEORETICAL BOTANY 



More than one pollen tube may develop in association with a single ovule 

 and more than one archegonium may be fertilized, but as there is only food 

 material for one to come to maturity, the others die off after a short period 

 of development. 



Embryogeny 



The fertilized, diploid nucleus of the oospore divides twice and the four 

 nuclei formed move to the bottom of the oospore (Fig. 689). There a third 



ROSETTE 

 CELLS 



•ROSETTE 

 CELLS 



VT 



SUSPENSORS 



B 



SECONDARY 

 SUSPENSORS 



EMBRYOS 



SUSPENSORS 



COTYLEDONS 



SECONDARY^ 

 SUSPENSORSr 



EMBRYOS - 



ROSETTE 

 CELLS 



SUSPENSORS 



EMBRYONAL CELLS 



Fig. 689. — Piiiiis sylvestris. Development of the embryo. A to E, Successive division of 

 the fertilized oosphere. F, Elongation of primary suspensors. G, Formation of 

 secondary suspensors and separation of four embryonal groups. H, Development of a 

 single embryo and multiplication of suspensor cells. J and K, Appearance of the 

 cotyledons and differentiation of embryonic axis. (A to E after Coulter and Chamberlain, 

 G to K ajter Biichholz.) 



nuclear division takes place and the eight nuclei arrange themselves in two 

 tiers of four, the lower four being cut off by walls. The upper, free nuclei 

 are separated only by imperfect walls and they take no further part in the 

 formation of the embr^^o. The lower cells divide once, so forming three tiers 

 of four cells each, and a final division of the lowermost nuclei completes the 



