CHAPTER XX 

 LEGUMES 



You will remember I told you something about 

 plants that take nitrogen out of the air and store 

 it in their roots. I promised then to tell you more 

 about them later. They are called "Legumes." 



Have you heard how plants use potash, phos- 

 phoric acid and nitrogen, and how the most difficult 

 to obtain is nitrogen? The plants that gather nitro- 

 gen from the air give it to us for just what the seed 

 cost, which surely is not very much. We know that 

 there is a great store of potash and phosphoric acid 

 already in the soil but it is locked up so the plants 

 cannot use it. We had a long talk about the gases 

 which decaying matter (called humus) gives off, 

 and how these gases unlock the stores of potash and 

 phosphoric acid so the plants can use them. So 

 nitrogen is the thing we need most next to humus. 



There are many plants which store nitrogen in 

 their roots : all clover, all beans, all peas, vetch, and 

 alfalfa. I hope you will not forget to save all the 

 pea and bean vines and bushes from your garden 



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