68 



ELEMENTARY STUDIES IN BOTANY 



something of the structure of the body that can resist the 

 drying air. It is evident that an ordinary filamentous alga, 

 with every cell freely exposed, could not endure long expos- 

 ure to the air. But the bodies of certain Algae are flat 



FIG. 51. Riccia: a group of floating Liverworts, showing the dorsal surface exposed 

 to light ; the flat body forks as it grows, and the axis of each branch is marked by 

 a deep groove, in the bottom of which the sex-organs (antheridia and archegonia) 

 occur. Photograph by LAND. 



plates of cells, and such bodies seem to have supplied the 

 start for Liverworts. A brief description of a liverwort 

 body will show how every fact is related to air exposure as 

 contrasted with water exposure. 



The body is compact ; that is, the cells are close together, 



