198 VEGETABLE PHYSIOLOGY 
roots of these plants grow down into soil which is infested 
with the mycelia of different fungi, with which they become 
entangled. The hyphe of the fungi continue to grow 
together with the root, and form an investment over it, 
which is in some cases met with in the form of an open 
network, and in others in that of a dense feltwork (fig. 98). 
The fungi in some cases perforate the external cells of the 
roots and form a network in the interior. From the out- 
side of the investing mantle hyphe grow out into the soil in 
a similar way to the root-hairs of ordinary plants. These 
take the place of the root-hairs, which cease to be developed, 
and serve the purposes of the roots as absorbing organs 
for the water and the salts of the soil. The fungus is bene- 
fited by drawing its own nutriment from the cells of the root 
into which it has penetrated. The fungoid web or mantle 
4 is known as a myco- 
rhiza; it is present 
not only on the roots 
of the Cupuliferz, but 
on those of Poplars, 
and many Heaths and 
Rhododendrons. 
A curious case of 
this kind of relation- 
ship is shown by 
Monotropa,a member 
of the Heath family 
, Which possesses no 
Fig, 98.—a, Eprpnytic Mycoruizas or Fa 
sylvatica (x 2); B, Tre or Root paderilce chlorophyll. Mono- 
DENUDED OF THE INVESTING MANTLE (x 80). 
(After Pfeffer.) tropa possesses a 
rhizome, from which 
rise sub-aerial stems from ten to twenty centimetres high, 
bearing succulent membranous leaves. From the rhizome 
are given off crowded masses of roots which are covered 
with a mycorhizal mycelium, and are embedded in humus. 
There being no chlorophyll apparatus, Monotropa is de- 
pendent entirely on the mycorhiza for its nourishment. 
B 
