72 



VETERINARY BACTERIOLOGY 



much enlarged and shows many involution forms. The other 

 organisms growing symbiotically within or upon the roots of 

 plants are all molds. They develop either upon the surface 

 of the root, forming a white, cottony, floccose covering, or they 

 grow in the tissues just below the epidermis. They sometimes 

 cause nodules to develop, as is the case with the Russian olive and 

 the alder, or they produce no characteristic overgrowth of tissues 



Fig. 39. Nodules on the root of a legume, Soy bean. (Moore, U. S. Dept. 



Agr.) 



at any one point, but are found quite uniformly present upon the 

 young growing roots. Certain trees, such as the oak and the 

 pine, particularly, when growing in nitrogen poor soils, show the 

 development of this mycorrhiza (Gr. fungus and root). It has 

 been shown that these molds are quite active in taking up free 

 nitrogen from the air and are of benefit to the plant upon which 

 they occur. 



