Bryophytes : Liverworts and Mosses 



467 



up in short chains. Each chamber is connected with the air by 

 epidermis, but the epidermal pores in them are chimney-like 



Fife. 284. Diagram of a small portion of a Marchantia thallus showing, above, the upper 

 epidermis with chimney-like openings and the air cavities containing the chlorenchyma. 

 Below are the water-containing tissue and the lower epidermis with a single rhizoid. 



openings and are incapable of closing as do the stomata of the 

 higher plants. The presence of a distinct epidermis having pores 

 is a third feature of plants which improves their chances of living 

 on land. 



(4) The ability to withstand drying. When the vegetative 

 cells of water plants are dried, the protoplasm dies at once ; but 

 a few of the liverworts, like many mosses and like Protococcus and 

 a few other algae, do not die when water is lost from the cells.. 

 Just what quality the protoplasm possesses that enables it to 

 withstand drying, it is at present impossible to say ; but some of 

 the liverworts that grow on trees and rocks possess this quality, 

 and certain mosses have to a remarkable degree the ability 

 to withstand drying. A fourth factor which enables some 

 plants to live in the land environment is the ability to with- 

 stand drying. 



(5) The production of light spores. At some point in the life 

 cycle of most land plants, spores- of small size and light weight 

 are produced. The food contained in these spores is largely oil 

 — the lightest form in which a given amount of energy may be 

 stored. Spores of this kind are readily carried scores of miles by 



