CRYPTOGAMS 



333 



that make up the lichen thallus would probably have to be 

 classified separately, as algae or fungi, respectively, but as 

 fructification is the generally accepted basis of classification, 

 and the plant body is too intimately permeated with both 

 kinds of tissue to be divided, each lichen body as a whole is 

 classed with its particular kind of fungus. The entire group, 

 on account of the distinctive characters that mark it, is 



473 



474 



FIGS. 473, 474. Fruticose lichens: 473, Usnea barbata, bearded lichen; 474, 

 Cladonia rangiferina, reindeer moss : A, sterile ; B, fruiting portion. 



placed in a separate order of its own. This includes three 

 principal divisions, distributed according to the shape of the 

 thallus, and its habit of growth : (1) Crustaceous, those that 

 adhere closely to the substratum, as if glued or inscribed on 

 it ; (2) Foliaceous, with a broad, more or less lobed and leaf- 

 like thallus that adheres loosely to the substratum by means 

 of rhizoids springing from its under surface ; (3) Fruticose, 

 with branching, stemlike thallus attached at the base like a 

 regularly rooting plant (Figs. 473, 474). Among these are 

 the Iceland moss, used as an article of food by man, and the 

 reindeer moss (Cladonia rangiferina), which is the chief sus- 

 tenance of the reindeer. 



