Normal Soil and Its Requirements 11 



cause of the true rust diseases. Saprophytic fungi 

 are those which depend for their food on the dead and 

 decaying organic matter in the soil. Between these 

 two extremes there are intermediaries. As an illus- 

 tration of a soil fungus may be taken the ordinary 

 blue mold, Penicillium expansum Lk. This organ- 

 ism is made up of colorless feeding threads techni- 

 cally known as hypha? or mycelium (fig. 2 b). The 

 spores, which correspond to the seed of higher plants, 

 are borne on short stalks which bear broomlike tufts 

 composed of chains of small bluish, round bodies, the 

 spores (fig. 2 a-c). 



Fungi differ from the higher plants in their nu- 

 trition and mode of reproduction. Fungi have no 

 green coloring matter, chlorophyll, and are thus 

 unable to manufacture their own carbon by the de- 

 composition of carbon dioxide as do green plants. 

 This is why fungi must depend for their supply of 

 carbon on dead organic matter or on the higher plants. 

 Unlike the green plants, fungi have no flowers and 

 reproduce by means of spores (fig. 2 g-h). It has 

 been estimated that over 61,000 species of fungi 

 have been found and described on the higher plants. 

 The Soil Bacteriologist however has scarcely touched 

 on the soil fungi. 



Fungi are classified according to the mode of spore 

 formation. In some the spores are formed by a 

 regular sexual union of a female egg known as oogon- 

 ium and of a male element, the antheridium (fig. 2 e, 

 i, k). The resultant fertilized spore egg is known as 

 oospore (fig. 2 f). The latter germinates by sending 



