LICHENS AND ALG^ 



193 





On the other hand, many fungi are injurious to man, as they 

 destroy large quantities of agricultural produce, timber, and 

 otlier substances, when 



Circumstances lavour -^- ^v - - ^s-^'^vT^^^^ . "^'^ .v^' ^, V 

 their development. 

 Among these we men- 

 tion the Blights which, 

 as Bunt and Smut, de- 

 stroy the grain in the 

 ear of Paddy, and the 

 Moulds which are so 

 difficult to combat in 

 the monsoon. 







A common fungus 

 in the plains of India 

 is the Geaster, a fungus 

 that has its fructifica- 

 tion in a double cover. 



The outer cover bursts and spreads star-like, the inner one opens 

 by a hole at its apex. 



Fiff. ll^. — Geasler. 



44. Lichens and Algae. 



The Lichens {Lkhenes) represent a certain class of fungi 

 which associate with another cryptogamic class, the Algae, to 

 have a common household (symbiosis). Like all green plants, 

 the Alga3, which are green, are capable of forming the substances 

 required for the building up of their tissue. Hence they live 

 also by themselves on stones, walls, trunks of trees, etc. The 

 fungus, however, is dependent on ready-made food. It takes 

 such from the Algse which it densely covers with its mycelium. 

 In return, the fungus supplies its purveyors with raw food (/. e., 

 water and minerals dissolved in it), protects them from exsicca- 

 tion and fastens them to the rock, or the trunk of a tree. The 

 Lichens, which are commonly known by their grey colour and 

 their crust-like, leafy or shrubby appearance, form with the Mosses 

 (page 191) the very outposts of vegetation, growing at the ex- 



13 



