188 Perspectives in Microbiology 



In some cases benefits have been reported from inocula- 

 tion of young trees with the fungus endophytes, and poor 

 development of trees in certain areas has been ascribed 

 to lack of the necessary fungi. One of these cases was re- 

 ported by Rayner and Neilson-Jones (35) for an area 

 known as the Wareham Heath in England. Inoculation 

 with mycorrhiza soil, or addition of compost, or steriliza- 

 tion and subsequent inoculation corrected the deficiency. 

 It was concluded that some biological factor limited de- 

 velopment of the fungi. The possibility that this factor 

 was an antibiotic active against the mycorrhizal fungi has 

 been proposed by Jefferys (18), Wright (48), and others 

 (2, 34). 



There is agreement that mycotrophy is important, that 

 it is of common occurrence, that it has significance to the 

 plant host, and that the fungus makes limited develop- 

 ment in the plant, controlled in some w^ay by it. This is 

 almost the limit of agreement. Whereas there is evidence 

 of some degree of specificity between the fungus species and 

 the plant with which it is associated, this may not be a 

 fixed relationship with all mycorrhizae, for it has been said 

 (20), "There are no mycorrhizal fungi, there is only, a 

 mycorrhizal state." 



In one of the recent reviews of mycotrophy, Kelley con- 

 cluded that the endotrophic type is most common. In this 

 type of association the fungus penetrates the cells where 

 the filaments undergo intracellular digestion, releasing 

 their contents. The fungus derives some materials from 

 the plant, and the plant obtains some substances from the 

 fungus, but the nature of the substances and their impor- 

 tance to the organism that receives them are obscure. 



The diversity of types of mycorrhizae, as well as the 

 variety of the plants and fungi involved, has contributed 

 to the confusion regarding the importance of the fungi 

 to the hosts. 



