198 PLANT LIFE 



owe their faculty of " fixing " free nitrogen 

 to the energy which the chlorophyll enables 

 them to obtain from the sunlight. This is 

 the motive power which enables the machinery 

 of the green leaf to maintain its output of 

 carbohydrate, and it is from this carbohydrate 

 that the power or energy is more immediately 

 derived which enables the bacillus to perform 

 the tremendous operation of forcing free 

 nitrogen into combination, and thus to build 

 up from the raw materials the stuff from which 

 protoplasm itself can be made. Although 

 the leguminous root ultimately profits by 

 its relations with the bacillus in thus ac- 

 quiring a costly food in exchange for a cheap 

 one, there is no indication of any degeneration 

 of leaf structure on the part of the flowering 

 plant. It even becomes almost unthinkable 

 that it could occur, inasmuch as the continuous 

 supply of carbohydrate from the green parts 

 is a prime condition of the nitrogenous 

 synthesis. The importance to the organic 

 world of these plants which bring nitrogen 

 into combination in a form that can be 

 utilised by living beings is overwhelming. 

 For apart from some means of maintaining 

 the supplies of nitrogenous food, life itself 

 would ultimately cease to be possible in the 

 world. 



There are many other instances of remark- 

 able associations of two or more plants, in 

 which each is in turn more or less parasitic 

 on the other, or, at the least, lives on the 



