HOW LEGUMES HELP THE FARMER 



flour, when combined with yeast, will make good bread. 

 About four fifths of the air consists of nitrogen, but, just 

 as the unground wheat cannot be used for bread, so this 

 nitrogen can not be used directly by plants as food because 

 it is not in the right form. The nitrogen must first unite 



with certain substances 

 in the soil and form what 

 are called nitrates before 

 the plant can use it for 

 food. 



Surplus of Nitrates. 

 The little swellings on 

 the clover root serve as 

 houses in which live 

 swarms of minute beings 

 called bacteria that 

 change the nitrogen of 

 the air into nitrates. 

 These not only supply 

 the clover plant on which 

 they live with the ni- 

 trates it needs for food, 

 but they furnish more 

 than the plant needs, and 

 so make the soil more 

 Even if the 



FIG. ,8.-Tubercles on clover roots. 



farmer mows down the clover and uses it for hay, or if 

 his cattle eat it off, the soil will be richer in nitrates than 

 it was before the clover was planted. 



Potash Needed The young clover plants begin to 

 supply nitrates to the soil when they have been growing 



