430 



BOTANY. 



A). In their development most ovules, although straight 

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

 upon then) selves (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 

 ill to 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 mayor may not contain four nuclei), 

 forming a common cavity containing many nuclei or young 



Fig. 306 — Di- gramraatic longitudinal sections of ovules. A, the straight ovule (or- 

 thiiiiopou^) ; A, the body of tlif ovule, with its embryo sac, em ; ai, the outer ovule 

 coat (primine) ; il, the inner coat (.■■. cundine) ; m, the micropyle ; c, the base of the 

 ovuie, where the coats arise, called also the clialaza ; f. the ovule stalk cr funiculus, 

 ,B.an inverted ovule (anatropous) ; the Ion" fu' icnlus,/, has f usi-d with the primino of 

 one side of the ovule and formed the rapne, ;■. P, a bent ovule (rampjlotropous).— 

 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 j)roper. 



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

 naire des Phanerogames angiospermes," by .Juliea Vesque, in Annals 

 des Sciences NatnrelUs, 1879. 



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

 cell, 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. 



