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General Botany 



Fig. 248 a. A fungus {Cordyceps) 

 parasitic on the pupa of the to- 

 bacco worm. 



building tissue and supplying energy. 

 The large surface exposed by the in- 

 numerable hyphae is obviously ad- 

 vantageous in making contact with 

 the food substances. 



When the fungus lives within or on 

 the tissues of another plant, a part 

 of its hyphae extends among or into 

 the living cells of the host, and the 

 food accumulated there becomes a 

 source of food to the fungus. In this 

 case also, by the secretion of enzymes, 

 external digestion may occur before 

 the food passes into the fungus 

 hyphae. The growth of the hyphae 

 through the cell walls of the host 

 plant comes about in some cases by 

 the liberation of enzymes that dis- 

 solve the walls ahead of the growing tip of the hypha, in others 

 by the mechanical breaking of the tissues. Fungi, like most 

 plants without chlorophyll, must have access to complex carbon 

 compounds for food and energy, and in some cases they must 

 have nitrogen compounds also. 



Conditions for growth. Many fungi grow best in partial shade. 

 Since they require a certain amount of moisture, fungi are usually 

 most abundant in damp places. The most rapid destruction of 

 organic matter also occurs in such situations. The decay of 

 wooden beams under porches and in mines, the rotting of fruits 

 and vegetables in cellars, and the disintegration of partially buried 

 railroad ties are familiar examples of the results of favorable 

 conditions for the growth of fungi. Bacteria also are present in 

 such situations, and their growth and activities may go along 

 with those of the fungi and hasten the final destruction. In the 

 desert, where drought and intense light hinder the growth of these 

 organisms, timbers may withstand exposure for centuries. 



