62 ELEMENTS OF AGRICULTURE 



their nitrogen. This gas is not taken up through the 

 leaves or stem, but through the roots. Rain water 

 washes the ammonia from the air into the soil, where 

 it may be changed to a form suitable for plant food. 

 The amount of nitrogen thus supplied to plants is, how- 

 ever, quite small. 



62. Nitrogen. — Some plants have the power of using 

 the nitrogen of the air for food. There are, however, 

 only a few varieties of plants that have this power, and 

 of them we shall have more to say later on. 



Questions 



1. From what source t do plants draw their supply of carbon? 

 2. How does carbon occur in the air? -3. In what form is car- 

 bon taken'in by plants? 4. In breathing, what element is taken 

 from the air by men and animals, and what returned to it? 

 5. What element is taken from the air by the leaves of plants, 

 and what returned? 6. Why are the leaves sometimes called 

 the lungs of plant*? 7. Why is it necessary to loosen up the 

 giound when planting seed? 8. What parts of plants take up 

 oxygen ? 

 nitrogen ? 



