244 THE BIOi:OGY OF FLOWERING PLANTS 



mycotrophic habits it is possible that the saprophytes have 

 had their origin. 



§ 3. Mycotrophic Plants 



The term mycorhiza was first used by Frank (1885) to 

 designate the association of 2i fungus with the root of a higher 

 plant. It is commonly regarded as a kind of symbiosis, by 

 which is meant an intimate partnership of two organisms 

 in which both partners benefit. But the details of mycorhiza 

 are so varied, and we know so little of their physiological 

 relations that it is not safe to assume mutual benefit or even 

 one-sided benefit in all cases. The term is somewhat 

 naturally used to cover the association in a plant like Coral- 

 lorhiza which has no roots but only a root-like rhizome, and 

 it is extended to plants in which the fungus inhabits shoot 

 structures which have no resemblance to a root at all, as 

 in the curious Japanese orchid, Gastrodia. Despite the 

 violence it does to etymology this usage is established, 

 though the term mycotrophic is more exact. 



Mycorhiza associations were divided by Frank into two 

 classes, ectotrophic and endotrophic. In the latter, typically 

 seen in the orchids, the fungus inhabits the root cortex ; 

 in the former it occurs as a mantle outside the root, and only 

 penetrates between the epidermal cells, as in the pine, the 

 beech, and many other forest trees. This distinction, 

 striking enough in extreme cases, cannot always be applied. 

 Intermediate types are known, and, even in typical cases 

 of the one or the other extreme, the fungus is not so sharply 

 localised as the terms imply. 



Mycorhiza is an extremely widespread phenomenon. 

 It is exhibited by all the orchids, by the autotrophic as well 

 as by the saprophytic, and by all the Ericaceae, in endotrophic 

 form ; the majority of our forest trees possess ectotrophic 

 mycorhiza. These are the best known cases, but it has been 

 shown by Janse (1897), Stahl (1900) and Gallaud (1905) that 

 most families include plants which more or less frequently 



