572 



BOTANY 



PART II 



sac and at the lower end three naked cells are thus formed. The two 

 remaining " POLAR NUCLEI " move towards one another in the middle 

 of the embryo-sac, and fuse to form the "SECONDARY NUCLEUS of 

 the embryo-sac." The three cells at the lower end are called the 

 ANTIPODAL CELLS ; they correspond to the vegetative prothallial cells, 

 which in Gymnosperms and in Gnetum fill the cavity of the embryo- 

 sac. The three cells at the micro- 

 pylar end constitute the "EGG 

 APPARATUS." Two of them are 

 similar and are termed the SYNER- 

 GIDAE, while the third, which pro- 

 jects farther into the cavity, is the 

 EGG -CELL or OVUM itself. The 

 synergidae assist in the passage 

 of the contents of the pollen-tube 

 into the embryo-sac. Here also 

 the process of reduction has gone 

 as far as possible ; in place of the 

 more or less numerous archegonia 

 of the gymnospermous macrospore 

 only a single egg-cell is present. 



FIG. 551. Ovary of Polygonum Convol- 

 vulus during fertilisation, fs, Stalk- 

 like base of ovary ; fu, funiculus ; cha 

 chalaza ; nu, nucellus ; mi, micro pyle 

 ii, inner, ie, outer integument ; e 

 embryo-sac ; ek, nucleus of embryo 

 sac ; ei, egg apparatus ; an, antipodal 

 cells ; g, style ; n, stigma ; p, pollen 

 grains ; ps, pollen - tubes. ( x 48. 

 After SCHENCK.) 



FIG. 552. Funkia ovata. Apex of nucellus, 

 showing part of embryo-sac and egg 

 apparatus before fertilisation ; o, egg-cell ; 

 s, synergidae. (x 390. After STRAS- 



BURUER.) 



The significance of the synergidae is difficult to determine unless they 

 are regarded as archegonia which have become sterile or, with TREUB 

 and PORSCH, as neck cells of an archegonium transformed to the 

 egg apparatus (Fig. 552). 



In some cases the mother cell of the embryo-sac does not undergo a tetrad 

 division, but forms only three or two daughter cells or is directly transformed into 

 the embryo-sac without dividing. The last is the case in Lilium, where the mature 

 embryo-sac contains the usual eight nuclei. In Cypripedium and Plumbagella, on 

 the other hand, the number of nuclei is reduced to four by the omission of the last 



