THE ENDOSPERM 



177 



said to begin with free nuclear division, followed by a wall cut- 

 ting off the mieropylar end of the sac ; and the same statement 

 in reference to Ceratophyllum has been disproved recently by 

 Strasburger. 49 The endosperm is said to develop only in the 

 antipodal chamber in Loranthus, Vacciniaceae, Verbenaceae, 

 Hebenstreitia (Selaginaceae), Bignoniaceae, and Acantliaceae. 

 In Trape.Ha (Oliver 10 ), a genus of the Pedaliaceae, although 

 the sac is not chambered by a wall, the endosperm develops only 

 in the lower two-thirds, a sort of diaphragm of thick-walled en- 

 dosperm-cells cutting off the broad mieropylar end of the sac. 



B 



C 



Fig. SO. — Ceratophyllum submermm. Development of endosperm and embryo. A, first 

 division of embryo, six cells in endosperm ; x 250 ; M, embryo and endosperm more 

 advanced ; x 250 ; C'-D, entire embryo seen from opposite sides, showing the two 

 cotyledons separate and I) nearly united ; x 50. — After Strasburgep.. 40 



Cases are also known in which more than two chambers are 

 formed in the embryo-sac and followed by ordinary cell-forma- 

 tion. For example, in Ceratophyllum (Strasburger 49 ) at the 

 first division of the primary endosperm nucleus the sac is 

 divided into two approximately equal chambers. The nucleus 

 in the antipodal chamber does not divide again, but at the next 

 division in the mieropylar chamber another wall across the sac 



