LIVERWORTS 395 



Bryophytes 



You know what moss is. You have seen it growing in 

 all sorts of places, and you have probably called things 

 moss which are not moss at all. People are likely to say 

 that any plant whose leaves and stems are not distinct is 

 a " kind of moss." But the stems and leaves of true 

 mosses are distinct, though they are usually very small. 

 True mosses form one of the divisions of bryophytes. The 

 other division is the liverworts. The liverworts are simpler 

 than the mosses and we will consider them first. 



73. Liverworts. — These plants grow where it is damp 

 and shady. They grow on decaying rock and on decay- 

 ing logs and sometimes on the soil itself. They have dis- 

 tinct under and upper surfaces. They are prostrate. In 

 this they are different from their relatives, the mosses, 

 which do not have distinct under and upper surfaces, even 

 though some of them are prostrate. 



The simplest liverworts are thought to be much like the 

 first plants which ever grew on the land. These simplest 

 liverworts are found on water or on mud which is left after 

 the water has disappeared. It is believed that plant life 

 began in the water. Occasionally pools of water in which 

 this early plant Hfe grew would dry up. It is believed that 

 some of these water forms acquired such structures that 

 they did not die as soon as such pools dried up ; they did 

 not need to be completely surrounded by water in order to 

 live ; they were able to live because they could absorb water 

 from the damp surface beneath and because they were pro- 

 tected on top by a structure which prevented the prompt 

 loss of this water by evaporation. Their structure enabled 

 them to retain water better than it could be retained by 



