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 or rind. Examined microscopically the 

 cells are found to contain enormous numbers of 



