CHAPTER XIV 



THE SIMPLEST LAND PLANTS : LIVERWORTS 

 AND MOSSES. THE PTERIDOPHYTA. 



HITHERTO we have been dealing entirely (except in 

 the case of the Fungi) with plants which live in water, 

 and get the whole of the raw materials of their food 

 supply from water and the substances dissolved in it. 

 But very far back in the history of the earth some 

 plants emerged from the water and established them- 

 selves on the land, henceforward getting their carbon 

 dioxide and their oxygen for respiration direct from 

 the air. These terrestrial plants have, in course of 

 time, dominated the surface of the earth, and, like 

 the terrestrial animals, have developed the most 

 complex structures. The most highly developed group 

 are the seed plants or flowering plants which are the 

 most completely adapted to land life. The history 

 of the evolution of the plant kingdom, beyond the 

 stage of the earliest land plants, is mainly a history 

 of increasing adjustment to terrestrial conditions. We 

 know nothing of how plants succeeded in first emerging 

 from the water, nor can we follow in detail the 

 course of their subsequent evolution. But by study- 

 ing the simplest land plants now existing, plants 

 which have become stabilised, so to speak, at an early 

 stage of adjustment to terrestrial conditions, we can 



