Liverworts and Mosses 273 



stand erect, but usually have their thalli in close contact 

 with the substrata on which they grow. In most forms the 

 thallus is a continuous plate of cells, but some forms have 

 prostrate stems with small leaves on either side. All of them 

 have chlorophyll and manufacture their own food. All the 

 forms have on their under surfaces small, hair like rhizoids 

 that anchor the plant and absorb water and minerals. 



Liverworts are widely distributed but are most numerous 

 in the tropics. A few of them are found on trees and rocks 

 and a few are found floating on water, but as a whole they 

 live on moist soil and in shaded situations. 



Reproduction among the liverworts takes place by means 

 of spores, produced either directly on the thallus or on special 

 branches. In many liverworts there are produced also special 

 bodies called gemma, (singular, gemma), which propagate the 

 plants vegetatively. 



The liverworts are supposed to be descended from plants 

 like the green algae, for it is thought that the simplest plants 

 existed first and that plant life as well as animal life had its 

 origin in the water. The liverworts may be considered, there- 

 fore, as a group of simple plants that exhibit some of the stages 

 through which plants pass in going from the water and taking 

 up their life upon the land. In this respect they can be com- 

 pared to the amphibious (Greek : amphi, double, and bios, 

 life ; i.e., life both on land and in water) frogs and salamanders 

 of the animal world. Just how a plant becomes adjusted to 

 its new environment, when it is forced to live on land because 

 of the drying up of the pool in which it grew, is a most inter- 

 esting question to consider. 



Living conditions of water and land plants contrasted. 

 The algae probably represent the remnants and derivatives 



