THE WORK OF ROOTS AND STEMS 71 



itself alone. They can only feed on it when it is united 

 with some other substance. And plants in general have 

 no power to bring about this union. 



So the work has to be done for them. The " free " 

 nitrogen is made ready for their use in the soil by 

 numberless tiny specks of living creatures the very 

 lowest and smallest and simplest kinds of life, either 

 vegetable or animal. They are called " Bacteria," and 

 weak and tiny as they are they have this task to carry 

 out. They have to capture the nitrogen gas, and to 

 unite it with some other substance, so that it may 

 become fit to be food for plants and animals. 



It is only certain kinds of these minute " Bacteria " 

 which have the power; and more particularly certain 

 kinds that feed largely on the roots of beans and clover 

 and other growths belonging to the same family, though 

 not on those alone. 



So the living specks of which we are thinking, hidden 

 away in the soil, are doing two things. They are feeding 

 on the roots of bean-plants or clover-plants ; and at the 

 same time they are busily making ready the food which 

 those bean-plants and clover-plants must have to keep 

 them in health. 



You see now what an important question it is 

 what kind of soil we put seeds into, year by year, whether 

 in gardens or on farm-lands. 



And now to come back to roots in general. 



The root grows downward away from the light, and 

 as it does so, gradually lengthening, its tip travels 

 gently round, hunting for food like a live thing. And, 

 of course, it is a live thing. The plant has life. 



