THE FUXGI 



255 



the soil, serves as food for the reindeer and is known 

 as " reindeer moss." 

 Most lichens grow 

 on the bark of trees, 

 on rocks, or soil 

 where they have lit- 

 tle moisture except 

 during rainfall, but 

 some grow where 

 the}' are constantly- 

 wet. Some of the 

 latter are gelati- 

 nous. Most of the 

 ■conspicuous lichens 

 are f oliaceous or else 

 have a thallus com- 

 posed of branching, 

 cylindrical, thread- 

 like portions. But 

 rnany species, often Fig. 180. Transverse Section through Thallus 

 less conspicuous, are °^ ^ ^'^^^"^ ^^^^^"^ fuliginosa). ( x 500.) 



crustaceous, grow- <'• cortical or epidermal layer ; g, gonidia ; 



mg as if they formed 



part of the bark or rock to which they are attached. 



PUCCIXIA, OXE OF THE BASIDIA FUXGI 



328. Occurrence. — Puccinia graminis, wheat rust, is 

 common on cultivated wheat and other grains and also 

 on many wild and cultivated grasses besides the grains. 

 Numerous species of rust are known. A rust may have 

 one, two, or three kinds of spores, and when three occur 



