484 



EEPEODUCTION. 



sac. During the subsequent development of the ovule the 

 embryonal sac continues to increase in size, often irregularly, 

 and displaces or obliterates by absorp- 

 tion many of the cells around it. 



1127. At an early period in the de- 

 velopment of the embryonal sac it is 

 completely filled with protoplasm con- 

 taining a cell-nucleus. This nucleus di- 

 vides, and the two new nuclei are soon 

 found at opposite ends of the sac, where 

 each divides into four nuclei. Between 

 the two groups of four nuclei there may 

 be a vacuole of considerable size. 



The next stage is marked by the pas- 

 sage of a nucleus from each extremit3- of 

 the embrj'onal sac towards its centre, 

 where they become united to form a sec- 

 ondary nucleus. 



1128. The nuclei at the lower end of 

 the sac become surrounded with other 



protoplasmic matter, and later by cell-walls ; they then consti- 



tute what have been termed the antipodal cells. At the upper 

 end of the sac, also, the three nuclei become surrounded by 



Fig. 199. Longitudinal section of theortliotropouB ovule of Polygonum divaricatum. 

 /«, funicnlns; te, tlie two integuments; nu, the nucellus, ■whose summit is prolonged 

 towards the mi(Top,vJe. mi ; se, the emhryoiial sac. (Strasburger.) 



F]a. 200. Polygonum divarioatum. Summit of the ovule with the apex of the em- 

 bryo sac, and the complete embryonal apparatus, e, the oospore; s, one of the syner- 

 gidae, the other being hidden from view. (Strasl>urger.) 



Fig. 201. Polygonum divaricatum. Summitof the ovule, showing the encroachment 

 of the embryo sac upon the adjoining cells. (Strasburger.) 



