Chapter 13 



MYCORRHIZAE AND MYCOTROPHY 



Our knowledge of the existence of a dual relationship of fungi 

 with the roots of green plants begins with the classic work of 

 Frank (1885). He regarded mycorrhizae* (literally, fungus 

 roots) as compound structures constituted of two components, a 

 fungus and a root. These components are associated in a nutri- 

 tional or mycotrophic relationship, and the structure produced by 

 their association is morphologically distinct, in the same sense that 

 a lichen is distinct from the alga and the fungus composing it. 

 These findings by Frank immediately stimulated others to under- 

 take studies on mycorrhizae, and interest in the problems that 

 have arisen has not flagged to the present day. Nevertheless no 

 problem involving fungi is so little appreciated and understood bv 

 mycologists today, and there does not appear to be any of greater 

 significance. Much of the work on mycorrhizae has been done 

 by persons with such divergent interests as foresters, silvicultur- 

 ists, physiologists, morphologists, pathologists, and cytologists, and 

 in consequence an overwhelmingly voluminous literature on my- 

 corrhizae has accumulated. An invaluable bibliograohv on the 

 subject, covering more than 900 typed pages, was prepared by 

 Kelly (1932). As a consequence of the numerous publications 

 it might be supposed that mycorrhizae are thoroughly understood, 

 but many phases of this subject still remain controversial. The 

 conflict of observations, opinions, and conclusions may be at- 

 tributed in part to the dangerous habit, even among scientists, of 

 making generalizations. Interested students and investigators will 

 find the monographs by Rayner (1927), Hatch (1937), and Bjork- 



* Frank (1885, p. 129): "Die ganze Korper ist also weder Baumwurzel 

 noch Pilze allein, sondern ahnlich wie die Thallus von Flechten, eine 

 Vereinigung zweier verschiedener Wesen zu einem einheitlichen morpho- 

 logischen Organ, welches vieleicht passend also Pilzwurzel, Mycorhiza, 

 bezeichnet werden kann." 



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