364 TRANSACTIONS AND PROCEEDINGS OF [Sess. lvi. 



As this membranous partition divides the embryo-sac into 

 an apical portion lying next the micropyle of the ovule, and 

 into a basal portion, in which latter the so-called antipodal 

 cells are developed, the apical and basal portions will 

 henceforward be called the micropylar and the antipodal 

 ones. 



To return to Strasburger's contention that the embryo-sac 

 is a macrospore : — Is it likely that an embryological-cell, such 

 as a macrospore, whose function it is to give rise to one pro- 

 thallus,will divide into two portions or cells quite independent 

 of one another ? By a supposed analogy to the microspore or 

 pollen-grain, the view was advanced, that the first division of 

 the nucleus of the embryo-sac-cell gave rise to a vegetative 

 and a reproductive part, the former corresponding to the 

 basal half of the embryo-sac, while the latter corresponded to 

 the apical half. But is the reproductive cell of a pollen-grain 

 independent of the vegetative cell ? Certainly not, for to the 

 vegetative cell falls the share of producing the pollen-tube, 

 while the reproductive cell is concerned in fertilisation. 



We have seen that the micropylar half of the embryo-sac 

 may lead an existence independent of the antipodal half, 

 a fact which compels one to regard the two halves of the sac 

 as homologues. 



One more question must be answered : Why does the 

 embryo-sac-cell, after the division of its nucleus, not lay down 

 a definite cell- wall, and separate into an apical and a basal 

 half ? One reason may be that the vacuole or vacuoles, 

 which arise in the micropylar and antipodal ends of the 

 embryo-sac-cell before its division, are shifted in some special 

 way either during or after karyokinesis into a position 

 midway between the two newly formed nuclei, i.e., into the 

 very place where normally a new cell-wall should be laid 

 down. Another reason may be this : — If the embryo-sac- 

 cell is a sporocyte, then its first division will correspond to 

 the first of the binary divisions of other sporocytes, e.g., 

 pollen-grains, and we know that in pollen-grains the second 

 of the binary divisions may follow upon the first, without 

 a cell-wall having been laid down after the first division. 

 A third reason has been fully explained at the bottom of the 

 previous page (363). 



In the antipodal end of the sac a small vacuole (fig. 19) 



