THE Alga; are water plants, being found both in fresh and salt water, and although the great majority of the fungi are land plants they are considered to have evolved from an algal stock. The Thallophytes, therefore, are essentially aquatic in character.
The remaining plants are typically land plants, and are classified in three large divisions, which are :—
The Bryophyta, which include the liverworts and mosses.
The Pteridophyta, which include ferns, horsetails andclub mosses.
The Spermaphyta, which include the conifers and the.
Through thesecan be traced a series of progressive adaptations to life on land. The Bryophyta and the Pteridophyta live in moist conditions and are dependent on the presence of external water for fertilization. The Spermaphyta, however, employ a method of fertilization which is independent of external water and also produce which are capable of passing unharmed through adverse conditions in a dormant condition. These two factors have been mainly responsible for the sucoess of the Spermaphyta which now form the dominant type of vegetation of the greater part of the earth ’s surface.