FUNCTION OF MYCORRH1ZAE 305 



Another endotrophic mycorrhizal relationship, which is of un- 

 usual interest and has been studied rather extensively, involves 

 the grasses, Lolhtm perenne and L. temulentum. The fungus in- 

 vades the growing point, penetrates the carpels, and has been 

 demonstrated to occupy the ovules and embryo. Sampson (1935) 

 called attention to the fact that fungus-free seed can be made to 

 produce fungus-free plants that set seed. On the other hand, seed 

 containing the endophyte may produce plants that again are 

 mycorrhizal. This fungus is not identified, but there are reasons 

 for believing it may be a smut. 



Function of mycorrhizae. Although knowledge of the exist- 

 ence of mycorrhizae dates back at least to the fourth century b.c. 

 [Kelly (1932)], definite information concerning their true struc- 

 tural nature may be said to begin with Frank's observations in 

 1885. In the years that followed, conjecture as to their function 

 was rife, and from the publication of Frank's classical studies to 

 the present, numerous theories on this subject have been advanced. 

 Of these only two have been accorded general acceptance. In 

 one theory mycorrhizae are regarded as pathological structures 

 induced by the parasitic action of the fungus upon the root tis- 

 sues. The other theory is that mycorrhizae are symbiotic struc- 

 tures that facilitate the absorption and utilization of organic ma- 

 terials, especially of organic nitrogen, contained in humus. It 

 appears that evidence in support of these theories may be best pre- 

 sented by a brief review of a few of the numerous publications 

 on mycorrhizae. 



Over 100 years ago the mode of nutrition of Monotropa hypo- 

 pitys, a flowering plant lacking chlorophyll, attracted the atten- 

 tion of botanists. This curious plant, classed as a saprophyte in 

 modern botanical textbooks, grows with its roots intermingled 

 with those of beeches, spruces, and other species of trees. In 

 consequence some workers regarded the Monotropa as a root 

 parasite, and thev noted that its roots were covered with "a whit- 

 ish, silky, somewhat fibrous material, connected with the decaying 

 leaves." The fungal nature of this material was first recognized 

 in 1832 by Elias Fries. Several early workers demonstrated that 

 Monotropa is not a root parasite by the simple expedient of trans- 

 planting and maintaining it apart from tree roots. In spite of this 

 fact, final settlement of the mode of its nutrition was deferred 

 until 1881, when Kamiensky (1881, 1882) again showed that 



