THE TREE—ITS ROOT-SYSTEM 97 
said to replace (fig. 25, f). These hyphe 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, 7m). 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. 
