ANGIOSPERMS. 



3*7 



the upper and lower group of cells there is still an unemployed nucleus (polar 

 nucleus}. These two nuclei move towards the middle of the embryo-sac and there 

 coalesce and form a larger nucleus (Fig. 319 VIII, sek}, which is now the nucleus of 



FIG. 319. Polygonum divaricatunt. Ovules and development of the embryo-sac. la longitudinal section through a 

 young ovary ; the ovule terminates the floral axis. Ib longitudinal section through a rudimentary ovule before the for- 

 mation of the integument ; em mother-cell of the embryo-sac (archesporium), t primary tapetal cell. // older stage, the 

 mother-cell of the embryo-sac has divided into two cells, in both of which the nucleus is in the act of dividing. /// mother- 

 cell of the embryo-sac divided into four (sporogenous mass of cells) ; the lowest of these cells e displaces the rest and 

 becomes the embryo-sac in IV; peh is the primary nucleus of the embryo-sac and has divided in V into two daughter- 

 nuclei, which in VI and VII form the egg-apparatus and the antipodal cells ; o the oosphere, s synergidae, g antipodal 

 cells. V III is a longitudinal section through a mature ovule with the inner integument it and the outer at, the nucellus 

 n and the vascular bundle gf entering the funiculus./; sek secondary nucleus in the embryo-sac. After Strasburger. 



the embryo- sac (secondary nucleus}. The perfected embryo-sac therefore contains 

 the egg-apparatus consisting of the two synergidae and the oosphere, the nucleus of 

 the embryo-sac and the antipodal cells, and these elements are found with slight 

 variations in all embryo-sacs. 



A comparison of Angiosperms with Gymnosperms shows that there is an almost 

 perfect agreement between them in the matter of the formation of the embryo-sac 

 (macrospore). The mother-cell of the embryo-sac in both Angiosperms and 



c c 2 



