THE TREE ITS ROOT-SYSTEM 97 



said to replace (fig. 25, /). These hyphas are extremely 

 fine tubes of a cellulose-like substance, filled with the 

 living protoplasm of the fungus, and possess the remark- 

 able property of being able to bore their way through 

 or between the cellulose walls of the roots. The fungus 

 attacks the plant about the second year, and it is not 

 difficult to find true root-hairs on the young root-system 

 when the apices are still free from the fungus mycelium. 

 The parts of the root attacked alter their form slightly ; 

 they grow more slowly in length, and assume a fleshy, 

 coral-like appearance (fig. 7, m). Such a fungus-clothed 

 root is called a mycorhiza, and the view is gaining ground 

 that the symbiosis between the fungus and the root is 

 of advantage to the oak. It has even been suggested 

 that the mycelium performs the functions of root-hairs 

 to the root, absorbing water and nutritive materials from 

 the soil and passing them on to the oak, in return for a 

 certain small proportion of organic substance which the 

 latter can well afford. At any rate, it may be that the 

 fungus hurries the decomposition of vegetable remains 

 in such a way that they become available to the roots 

 sooner than would otherwise be the case. The syste- 

 matic position of these remarkable fungi is not yet as- 

 certained, but there is some evidence for the view that 

 the mycelium is that of a truffle, though the question is 

 still an open one. 



