256 THE BIOLOGY OF FLOWERING PLANTS 



are sometimes spoken of as being parasitic on tlieir 

 endophytic fungi, a description which scarcely helps 

 us to an understanding of the relation. Only in the 

 Ericaceae have we any real grasp of the situation — and not 

 even here of the causation of root formation. An explana- 

 tion in other cases must wait on more and very difficult 

 research. 



Other Cases. — Endophytic mycorhiza has been described 

 for many other plants, e.g. by Stahl (1900), Janse (1897), and 

 Gallaud (1905). The fungi are hyphomycetous, without 



Fig. 33. — Mycorhiza of black bryony (Tatnus communis) ; long, section 

 through root. (After Gallaud.) 



cross walls, and infect the roots through the epiderm. They 

 spread both inter- and intra-cellularly, and typically show 

 hyphae ending in fine branches the ends of which are con- 

 verted by the host plasma into lumps or " sporangioles " 

 which are digested (Fig. 33). Of their importance for the 

 plant little is known. In most cases it is probable that the 

 fungus is not necessary to the plant. We must remember 

 that the conditions for the infection of a root by fungi are 

 extraordinarily favourable in humus soils, where a rich 

 fungus flora exists. There is doubtless a constant struggle 



