CHAPTER TWENTY 



LIVERWORTS AND MOSSES 



Fig. i6i. 



A commuii liverwort (Marckantia), showing thallus, cupules, and 

 reproductive branches. 



The largest of the mosses and liverworts never attain a 

 height or length of more than a few inches, and they are of 

 very simple structure in comparison with the flowerixLg plants. 

 In contrast with the algae, which on the whole are water 

 plants, mosses and liverworts for the most part live on land. 

 The passing of plants from a water to a land habitat is one of 

 the notable steps in the development of the plant kingdom, 

 and in connection with the study of this group we shall con- 

 trast the environments of land and water plants and consider 

 the modifications in structure that accompany the passing of 

 plants from the water to a land habitat. 



The liverworts. The body of a liverwort is flat and leaflike 

 and is called a thallus (plural, thalli) . It may be from one to 

 several cell layers in thickness. It grows at the tip, and 

 usually branches by forking at intervals. Liverworts do not 



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