64 



PRACTICAL BOTANY. 



the vesicle within, more enlarged). The materials of tliis 

 vesicle are taken from the cytoUast, which consists of 

 globular atoms, contained in the sac. The embryonic 

 vesicle resembles all other new cells. 



Let us trace its development after fertilization in one or 

 more ovules of an oxogen. After attaining a certain size, 

 tlie vesicle divides by a cross-partition into two cells 

 (Cut XII., Fig. 3), and the lower of these into another 

 pair (Fig. 4). One cell of this pair continues the process 

 of division in two directions (Fig. 5), and the resulting 

 cells do the same, until the mass of cells assumes the out- 

 line of a rudimentary embryo, its upper extremity repre- 

 senting the radicle, in. form nearly cylindrical, and its 

 lower extremity the cotyledons under the form of a notch 

 (Fig. 6). Gradual changes in the aspect of this embryo 

 are shown in Figs. 7 and 8 and 9. The figures are, of 

 course, all magnified. In the Asclepiads, the masses of 

 cohering pollen-grains, dislodged in due time from their 

 anther-cells and brought near the base of the stigma, pro- 

 duce a great many tubes, which penetrate the base of 

 the stigma (Fig. 10). The fertilization of the naked 

 ovules of the Gymnosperms usually leads to the pro- 

 duction of several embryos, which, however, are com- 

 monly all but one abortive. 



Cut XII 



