304 FOUNDATIONS OF BOTANY 



generation is still very prominent in the life of the plant. 

 Ordinary ferns show us the sexual generation existing only 

 as a tiny independent organism, living on food materials 

 which it derives from the earth and air. In the Salvinia 

 it is reduced to microscopic size and is wholly dependent 

 on the parent-plant for support. Among seed-plants the 

 sexual generation is so short-lived, so microscopic, and so 

 largely enclosed by the tissues of the flower that it is com- 

 paratively hard to demonstrate that it exists. 



The fact that the life history of so many of the classes 

 of plants embraces a sexual stage, in which an egg-cell is 

 fertilized by some sort of specialized cell produced wholly 

 for use in fertilization, tends strongly to show the com- 

 mon origin of the plants of all such classes. We have 

 reason to believe, from the evidence afforded by fossils, 

 that plants which have only a sexual generation are 

 among the oldest on the earth. It is therefore likely that 

 those which spend the least portion of their entire life in 

 the sexual condition were among the latest of plants to 

 appear. Then, too, those which have the least developed 

 sexual generation are among the latest of plants. Judged 

 by these tests the angiosperms must be the most recently 

 developed of all plants. 



If one were to attempt to arrange all the classes of 

 existing plants in a sort of branching series to show the 

 way in which the higher plants have actually descended 

 from the lower, he would probably put some one of the 

 green algae at the bottom and the angiosperms at the top 

 of the series. 



376. The Oldest Angiosperms. It is impossible to give 

 any of the reasons for the statements of this section 



