194 PLANT LIFE 
phytes, and it is reasonable to conclude that 
the loss of the green leaves and all the 
structural change consequent on their abor- 
tion is directly connected with the growing 
ability of the saprophytic plants to develop 
the physiological faculty of utilising the 
resources thus rendered available. They 
come more and more to depend exclusively 
on the nutritive processes of fungi, not only 
for their carbohydrate kind of food but for 
the still more complex nitrogenous nutriment 
as well. Of course, the decaying leaves and 
‘other vegetable matter in the soil maintain 
a plentiful and practically continuous supply 
of carbonaceous food which is constantly at 
the disposal of those organisms which are 
adapted to make use of it. There is little 
doubt also that during the decomposition 
of the carbonaceous humus free nitrogen is 
sometimes forced into combination with other 
elements, either by micro-organisms, or myco- 
rhiza, or both, and so is rendered available 
for the higher plants. 
This way of looking at the matter fits in 
with the very remarkable nutritive processes 
so characteristic of the leguminous plants of 
which the peas and clovers are representative 
examples. If one of these plants be dug up 
(Fig. 22), its roots will be seen to bear nodular, 
or wart-like, swellings. These swellings are 
due to luxuriant growth of the tissues of the 
cortex orrind. Examined microscopically the 
cells are found to contain enormous numbers of 
