226 FORMATION OF PROTEINS 



The roots of all these humus-loving saprophytes and green 

 semi-saprophytes possess few or no absorptive root-hairs, but 

 are associated with the mycelium of certain fungi present in the 

 humus : the associated fungus and root is termed mycorhiza. In 

 ericas, orchids and some other plants the mycorhiza is endophytic, 

 the fungus living partially within the cortex of the root, while in 

 beech and most Cupuliferae the fungus clings to and covers the 

 surface of the fine rootlets with a web-like mantle of mycelium 

 from which separate hair-like hyphse grow out into the humus 

 and absorb portions of it : the latter type is spoken of as an 

 epiphytic mycorhiza. 



It is probable that some of the organic constituents of the 

 humus are dissolved by the fungus, and, with the other absorbed 

 coristituents of the soil, are finally transmitted to the plant with 

 which it lives in union. The fungus thus appears to act as a 

 beneficial absorptive agent, and without its aid the plant does 

 not thrive ; beech and pine seedlings are found to grow feebly, 

 and die off altogether after a time, in forest soil which has 

 been subjected* to. boiling water or steam so as to kill the fungus. 



As the plants of this class possessing green leaves have no 

 absolute need of carbohydrates, it is possible that the fungus 

 is concerned mainly with the absorption and transmission of 

 ammoniacal and organic nitrogen compounds, as well as sub- 

 stances containing the ash-constituents of the plant. 



