FUNGI: THE LICHENS 



271 



of mineral and nitrogenous substances, protects the alga during 

 dry seasons and holds it in place on steep slopes. Many lichens 



Fig. 234. 

 Foliaceous lichen (Physcia stellaris). Natural size. 



are multiplied and propagated naturally by small specialized 

 bits of the lichen thallus (soredia) 

 which become separated from the 

 main body. The fruiting stage, 

 however, is that of the fungus. 

 The fruit of the perfect stage in 

 nearly all of the lichens is that of 

 the sac fungi with which they are 

 classed. There are a few tropical 

 forms with basidium fruit fungi. A 

 large number of the lichen sac fungi 

 have fruit bodies like those of the 

 black fungi, while in many others they 

 are like the cup fungi. Other pecul- 

 iarities of the lichens can be noted 

 after the study of a few forms. 



433. The foliaceous lichens. These are leaf-like, and grow 

 on rocks, fences, tree trunks, or on the ground, where they are more 



Fig. 235. 



Much enlarged section of portion 

 of lining layer, showing the asci (i, 

 2, 3, 4) with their contained spores. 

 (After Sachs.) 



