THE PLANT AND THE ATMOSPHERE 47 



fumeroles also contain ammonia, which may be due to the action 

 of water on nitrides. 



Ammonia gas is absorbed by the foliage of plants, as has been 

 shown by experiments such as the following of Peters and Sachs. 1 

 The stem of a bean plant was cemented under a bell jar. The 

 leaves and foliage were within the jar, while the roots and soil 

 were outside. The plant was supplied through tubes with air 

 mixed with 4-5 per cent, carbon dioxide. Another plant in a 

 similar apparatus was supplied with the same gases, but they 

 were passed through a dilute solution of carbonate of ammonia, 

 which gives off ammonia. After two months, the plant supplied 

 with ammonia weighed, when dried thoroughly, 6.74 grams, and 

 contained 0.208 gram nitrogen; the other plant weighed 4.14 

 grams, and contained 0.106 gram nitrogen. The gain of nitrogen 

 must have been caused by the absorption of ammonia by the 

 foliage of the plant. If the entire plant and the soil in which it 

 grew had been placed in the bell jar, ammonia would have been 

 absorbed by the soil and presented to the roots. But the arrange- 

 ment of the experiment eliminated this possibility, since the soil 

 and roots did not come in contact with the ammonia at all. 



The ammonia of the atmosphere is in such small quantity that 

 it has practically no effect upon plants. This has been shown by 

 experiments such as the following: Hellriegel 2 grew lupines in 

 sterilized sand supplied with all plant food except nitrogen. The 

 nitrogen content of both seed and sand had been previously ascer- 

 tained by analysis. After the plants had reached their full 

 development, both plants and soil were subjected to analysis, and 

 the amount of nitrogen found was .007 gram less than was present 

 in the seeds planted and in the original soil. The plants, there- 

 fore, had lost a small amount of nitrogen, instead of gaining any 

 from the free nitrogen, or from the ammonia of the air. 



Nitric Acid. Nitric acid occurs in the air, probably in com- 

 bination with ammonia. It is formed by electrical discharges 

 (lightning). The quantity of nitric acid in the air is very small, 



1 Johnson, How Crops Feed, p. 56. 

 - Exp. Sta. Record, 5, 844. 



