FUNGI 



159 



balls; but it is thought that a basidium is represented also 

 in the life-history of the rusts, and hence they are now 

 included among the Basidiomycetes. This supposed ba- 

 sidium of the rust is the little filament produced by the 

 winter spore, which sends out branches that bear the small 

 early spring spores ( 84). 



88. Mycorhiza. This name means root-fungus, and 

 refers to an association that exists between certain Fungi 

 of the soil and the roots of higher plants. It was thought 

 once that this association of fungus and root occurred only 

 in connection with a limited number of higher plants, 

 such as orchids, oaks, heath plants, etc.; but more recent 

 study indicates that probably the large majority of vascular 

 plants, that is, plants with true roots, have developed this 

 relation to a soil fungus, the water-plants being excepted. 

 It has been found that the humus soil of forests is in large 

 part "a living mass of innumerable filamentous Fungi." 



It is of advantage to roots to relate 

 themselves to this great network 

 of filaments, which are already in 

 the best relations for absorption; 

 and those plants which are unable 

 to do this are at a disadvantage in 

 the competition for the nutrient 

 materials of the forest soil. It is 

 doubtful whether many vascular 

 green plants can absorb from the 

 soil enough for their needs with- 

 out this assistance; and if this is 

 true, the mycorhiza Fungi become 

 of vital importance in the nutri- 

 tion of such plants. The delicate 

 branching filaments of the mycelium 



either enwrap the rootlets with a jacket of interwoven threads 

 (Fig. 153), or occur within the cortical cells of the root. 



FIG. 153. Mycorhiza: the tip 

 of a beech rootlet enmeshed 

 by a soil fungus. After 

 FRANK. 



