SECT. II 



m- 



PHANEEOGAMIA 



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455 



The nucleus of the embryo-sac divides into two. Of these, one moves towards 

 the upper micropylar pole, the other towards the lower or chalazal pole. Each 

 nucleus then gives rise by repeated division to four nuclei, around three of which 

 protoplasm becomes aggregated, while the remaining two nuclei, withdrawing 

 towards the centre of the embryo-sac, meet and fuse into the definitive or secondary 

 nucleus of the embryo-sac. 



The three naked cells at the micropylar end develop into the egg-apparatus, 

 the three at the chalazal end into the antipodal cells. 



Fertilisation. — From the pollen-grains conveyed to the stigma by 

 the wind or by means of insects, pollen-tubes are developed which 



Fig. 387. — Orchis pollens, ovule. /, Funi- Fig. 3S8. — Ovary of Polygonum Convolvulus during fertil- 



culus ; ii, ie, integuments ; r,i, micro- 

 pyle ; r, raphe ; I, air - cavity ; os, 

 egg-apparatus ; a, antipodal cells ; 

 c, embryo - sac with nucleus, «.. 

 (Magnified.) 



isation. fs, Stalk-like base of ovary ; fu, funiculus ; 

 elm, chalaza ; nu, nucellus ; mi, micropyle ; ii, 

 inner, ie, outer integument ; e, embryo - sac ; ek, 

 nucleus of embryo-sac ; ei, egg-apparatus ; an, anti- 

 podal cells ; g, style ; n, stigma ; p, pollen-grains ; 

 ps, pollen -tubes, (x 48.) 



penetrate the canal or loose parenchyma of the style (Fig. 388). The 

 tubes increase in length until one comes in contact with the synergidse 

 (Fig. 389). One of the generative cells is then transferred through 

 the synergidse into the egg-cell, whereupon fertilisation is effected, as 

 in all cases, by the fusion of the two cells. After fertilisation has 

 taken place, the synergidae undergo dissolution, apparently being 

 absorbed by the fertilised egg. The egg itself becomes invested with 



