THE FEMALE GAMETOPHYTE 



119 



sequence then is as follows: megaspore mother cell, primary 2-nu- 

 cleate stage, primary 4-nucleate, secondary 2-nucleate, secondary 

 4-nucleate, and last of all the S-nucleate stage. 



Fig. 76. Development of embryo sac in Fritillaria persica. A, l.s. nucellus, show- 

 ing megaspore mother cell in prophase of Meiosis I. B, two-nucleate stage. C, 

 primary four-nucleate stage. D, megaspore nuclei, showing 1 +3 arrangement. 

 E, megaspore nuclei dividing. F, same, showing fusion of three chalazal spin- 

 dles. G, telophase of same division. H, secondary four-nucleate stage in which 

 the two micropylar nuclei are haploid and chalazal nuclei are triploid. 7, four 

 nuclei dividing to form eight. J, eight-nucleate embryo sac. (After Bambacioni, 

 1928a.) 



Normally all the 4 megaspore nuclei are of the same size, but in 

 some plants the micropylar nucleus is the largest and the other 3 

 nuclei are considerably smaller. When this happens, the nuclei of 



