PHANEROGAMIA. 215 
has not been detected. In either case the pollen-cell de- 
velops a tubular filament, sometimes of great length. If, 
now, such a germinating pollen-cell happens to be favora- 
bly placed near to an ovule, the pollen-tube may penetrate 
it and come in contact with the germ-cell. The protoplasm 
of the tube then unites with that of the germ-cell, and fer- 
tilization is complete. 
457. The fertilized germ-cell soon begins growing and 
dividing, producing in a short time a many-celled body— 
the embryo-plant. The embryo during its growth is nour- 
ished by the surrounding cells of the first stage, here called 
the endosperm. While the embryo has been growing, the 
covering of the ovule (one or two cellular coats) becomes 
gradually harder and firmer; finally the growth of the em- 
bryo stops, and the ovule containing it separates from its 
supporting fruit-leaf as a ripe seed. 
458. After a longer or shorter period of rest, the little 
plant in the seed resumes its growth, the necessary condi- 
tions being the proper heat and moisture. It is at first 
quite simple, consisting of a little root and stem and a few 
small leaves, but with the development of each succeeding 
leaf it becomes more like the adult plant. 
459. The flowering plants are separated into two classes, 
viz.: 
1, Ovules on an open fruit-leaf—GyMNosPERMa. 
2. Ovules enclosed within a closed fruit-leaf—ANGIOSPERM&. 
Crass I. Gymyosprrmz (the G@ymnosperms). 
460. These are plants with solid stems, which bear in 
most cases small, simple, narrow leaves with parallel veins. 
Most of them are large trees, and all are terrestrial and 
