( 20 ) 
in the following way : a grain of pollen, from one of the stamens, 
is deposited upon the upper extremity (the stigma) of the 
pistil, the moisture of which stimulates an outgrowth from the 
pollen-grain of a tube-like character — the pollen-tube, which 
makes its way, by growth, down through the loose cellular tissue 
composing the shaft or style of the pistil, until, finally, it pene¬ 
trates through the foramen of the ovule, and comes to lie in close 
contact with the apex of the nucleus of the ovule, just outside of 
the embryonal sac, and close to the embryonal vesicle.* With this 
latter, doubtless, the protoplasm of the pollen-tube comes into 
actual contact, whereby the protoplasm of the embryonal vesicle 
is incited to develope. This embryonal vesicle, it must be re¬ 
membered, is merely a single unit of protoplasm, corresponding 
to the single cell of the bacterium, the development of which by 
simple enlargement, constriction, and division into two has al¬ 
ready been described. This similar single cell in the higher plant 
enlarges and subdivides in precisely the same way, but the new 
cell-units, instead of falling apart, remain bound in close apposi¬ 
tion, and through their aggregation eventually form living masses 
of the most varying shapes and dimensions. To describe the pro¬ 
cess a little more in detail, the first cell of the germ of the coming 
plant—the embryonal vesicle—enlarges and divides into two cells, 
each of these two then grow and subdivide, making four, and by 
a continuance of this process a protoplasmic chain is formed, the 
terminal cells of which, after a certain length has been reached, 
then beginning to put out their offspring in three directions, 
whereby the germ, or embryo as it now comes to be called, ac¬ 
quires length, breadth, and thickness. In a little while the new¬ 
ly-forming cells cease to cohere along a certain line, or, in other 
words, the mass of the embryo in its later growth developes as 
two halves, which lie flattened out upon each other, ever curling 
more and more as restricted by the narrow confines of the ovule.f 
The protoplasmic chain spoken of corresponds to the little stem 
of the embryo or plantlet, while the separate halves become .the 
leaflets or cotyledons of the young plant. We have seen, now, 
how through fertilization of the ovule the primitive germ-cell has 
* Fig. 8. t Fig. 9. 
