XIX.] 



BOTANY. 



75 



pletely inverted, when the micropyle, instead of being 

 distant from the placenta, is brought into proximity to 

 it, and the base of the nucleus is at the top of the 

 ovule. In this last case the vascular bundles from the 

 placenta run up the side of the ovule to the base of 

 the nucleus. 



1 1 6. In the axis of the nucleus, a cavity lined with 

 a delicate membrane (the embryo sac) containing 

 protoplasm, appears. Within this sac again near its 

 top a dark spot is seen (germinal vesicle), which, 

 after the application of the tip of the pollen tube to 



FIG. 55. Longitudinal section of ovule of heartsease : a, placenta; Z>, outer 

 coat ; c, inner coat ; d, nucleus ; e, embryo sac, with the germinal vesicle 

 at its small end ; ./", micropyle ; g, end of pollen-tubevery much enlarged. 



the nucleus, acquires a cellulose coat, and becomes a 

 cell. This cell, by division (Par. 13), gives origin 

 to a filament, from the end of which the embryo Is 

 developed. 



