Kelley — 8 — Mycotrophy 



principle, Bernard's successor, Magrou, and his compatriot, Cos- 

 TANTiN, have developed an hypothesis of perennism by which they 

 attempt to account for existence of perennial plants on a symbiotic 

 basis. 



Symbiosis in Lolium: — Another phase of mycotrophic study 

 dealt with fungal infection of seeds, particularly of the seed-fruits 

 or caryopses of Lolium, a genus of grasses. Discovered by Vogl 

 in 1897, the constant presence of hyphae in the hyaline layer of the 

 caryopsis and typical stages of digestion, are curious phenomena that 

 have nevertheless been established by repeated researches, especially 

 at the hands of McLennan in Australia. The endophyte also occurs, 

 according to Neill (1940) in leaves of Lolium but not in those of 

 other pasture grasses. 



Obligate Mycotrophy in Heaths: — Infection of seeds of 

 heaths, especially of Calhina, has likewise been reported, particularly 

 by Rayner; indeed, practically all tissues of the plant were said to 

 be invaded by the otherwise mycotrophic fungus. Rayner claimed 

 that mycelium present in the seed-coat of Calluna grows into the 

 developing plantlet so that a sterile culture of this heath can not be 

 obtained. This assertion has been challenged by Knudson and by 

 Freisleben. According to Freisleben (1935), the fungus causes 

 an amelioration of soil conditions in which the heath grows and does 

 not directly affect life of the heath. 



Identity of the Mycorrhizal Fungi: — The specific identity of 

 mycotrophic fungi has proved more puzzling than might at first be 

 suspected. It would seem that sporophores directly attached to tree 

 roots might be safely considered the mycorrhizal fungi of these hosts. 

 Constant association of truffles with tree roots furnished the incen- 

 tive for Frank's study of the mycorrhiza, and there are many other 

 such associations, as, for example, Heheloma with birch. In many 

 cases rhizomorphs have been traced from sporophore to mycorrhiza 

 and the associated fungus has been termed mycorrhizal, but such as- 

 sociations may actually be the result of a secondary infection. Hence 

 the numerous citations of mycorrhizal fungi based on connection 

 of sporophore with mycorrhiza are not necessarily valid. 



Isolation of Mycorrhizal Fungi: — Isolating the fungus directly 

 from the mycotrophic organ has proved, in most cases, impracticable ; 

 and the usual method of identifying the fungus in question is to 

 grow a suspected fungus in pure culture, inoculate it into a sterile 



