s 



DESCRIPTIVE BOTANY. 



the whole frond itself, rolled inwards. The lower 

 tribes of cryptogamic plants, included in the division 

 " Cellulares," are very homogeneous in their struc- 

 ture, and of different degrees of consistency from 

 highly gelatinous, to tough and leathery. When they 

 consist of a plane membranous lamina, as in the Lichens, 

 this is termed a " thallus " (fig. 76.) ; but when more 



or less branched, the name of frond is retained. They 

 are either terrestrial, aquatic, or marine. Many of 

 them are parasitic, seldom green, and without stomata. 



