SECT. II 



PHANEROGAMIA 



511 



einbryo-sac and at the lower eud three naked cells are thus 

 remaining " tolar nuclei" move towards one another in 

 embryo-sac, and fuse to form the "secondauy nucleus of the 

 three cells at the lower end are called the antifodal cells ; 

 the vegetative prothallial cells, which in Gymnosperms and 

 cavity of the embryo-sac. The three cells at the micropylar 

 EGG-APi'AKATUS. Two of them are similar and are termed the 



formed. The two 

 the middle of the 

 embryo-sac." The 

 they correspond to 

 in Gnetuvi fill the 

 end constitute the 

 SYNERGIDAE, while 



et 



an- 



cfia- 







Fia. 473. — Ovary of Polygonum, Convol- 

 vulus during fertilisation, /s, Stalk- 

 lil^e base of ovary ; fu, funiculus ; cha, 

 chalaza ; nu, nncellus ; mi, micropyle ; 

 a, inner, ?>, oiitw integument ; e, 

 embryo-sac ; ck, nucleus of embryo- 

 sac ; ei, «gg-apparatus ; an, antipodal 

 cells; g, style; n, stigma; j), pollen- 

 grains ; jw, pollen-tubes. (X 48.) 



Fio. 474. — Ovule of Ulmus pedunnilata. es, Embryo- 

 sac ; in, micropyle ; ch, chalaza ; t, iDocket-like space 

 between the integuments. The pollen-tube, jw, pene- 

 trates directly through the two integuments and 

 reaches the apex of the nucellus, (After Nawaschin.) 



the third, which projects farther into the cavity, is the egg-cell or ovum itself. 

 The synergidae assist in the passage of tlie 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 gymuospermous macrospore 

 only a single egg-cell is present. The significance of the synergidae is difficult to 

 determine unless they are regarded as archegonia which have become sterile. 



The microspores, which cannot reach the macrospore directly, germinate on the 

 stigma (Fig. 471). The pollen-tube penetrates for the length of the style, and as 

 a rule the tip enters the microp/le of an ovule and so reaches the apex of the 

 nucellus. Of late years a number of exceptions to this usual course have become 



