420 



BOTANY. 



A). In their development most ovules, although straight 

 (Fig. 306, A] at first, become afterward more or less curved 

 upon themselves (Fig. 306, B and C}. 



The development of the embryo sac takes place in a much 

 simpler way in Angiosperms than in Gymnosperms.* An 

 axial cell enlarges greatly, becoming thus the young embryo- 

 sac (Fig. 306, em). In preparation for fertilization, it divides 

 into a row of several (3-6) cells, the uppermost of which 

 forms four nuclei, one of which becomes the germ-cell. 

 By the absorption of the cell wall, the upper cell fuses 

 with the second (which may or may not contain four nuclei), 

 forming a common cavity containing many nuclei or young 



Fig. 806. Diagrammatic longitudinal sections of ovules. A, the straight ovule (or- 

 thotropous) ; k, the body of the ovule, with its embryo sac, em ; at, the outer ovule 

 coat (primine) ; it, the iniier coat (*< cundine) ; m, the micropyle ; c, the base of the 

 ovule, where th coats arise, called also the cliala/.a; /, the ovule stalk or I'uniciilus. 

 .B.an inverted ovule (anatropous) ; the long funicnlus,/, has fused with the primine of 

 one side of the ovule and formed the raphe, r. C, a bent ovule (campylotropous). 

 After Prantl. 



cells, several of which, including the Germ-Cell, remain at 

 the top, the others (Antipodal Cells) occupying the lower 

 part. No endosperm is to be seen at this stage, f 



The fertilization of the germ-cell involves two operations, 

 viz., Pollination i.e., the deposition of the pollen upon the 

 stigma, and Fertilization proper. 



* See " Nouvelles Recherches sur le developpement du sac embryon- 

 naire des Phanerogames angiospermes," by Julien Vesque, in Annales 

 des Sciences Naturettes, 1879. 



t The endosperm, which here forms after fertilization of the germ- 

 oell, may be regarded as a belated piothallium. It is here no longer 

 necessary for the prothallium to precede the formation of the germ- 

 cell ; there is consequently a considerable retardation in its develop- 

 ment. 



