Chapter VIII. 



RELATION OF PLANTS TO ATMOSPHERIC NITROGEN. 



IN GENERAL. 



If the atmosphere varied largely in its chemical constituents, this 

 Avould doubtless have an appreciable influence on vegetation. Labo- 

 rious studies at Montsouris and elsewhere have shown that there is 

 a measurable variation in the quantity of ozone, so called, of ammonia, 

 and of carbonic acid gas, and Morley, at Cleveland, has shown an 

 appreciable, but very slight, systematic variation in the proportions 

 of nitrogen and oxygen. But all these variations are so small as 

 comj^ared Avith the variations in the quantity of air brought to the 

 jDlants by the wind, that their influence on vegetation, if any, can 

 not be separated from that of the wind, and is probably entirely 

 inappreciable as compared with other influences. 



On the other hand, the general fact that plants must have nitrogen 

 in order to produce albuminous and other nitrogenous compounds 

 has long been apparent. The question how to furnish this nitrogen 

 to the plants in such a chemical form that it can be readily assim- 

 ilated by the cells has undoubtedly been, consciously or unconsciously, 

 the problem of the agriculturist for many ages. Without nitrogen, 

 which is usually supposed to be furnished by fertilizers, manures, 

 rich soils, or the alluvial deposits of the rivers, no nutritious seeds 

 are formed, and the more molecules of nitrogen that we can force the 

 plant to take up into its tissues the more and better seed we may 

 expect to obtain in the harvest. 



THE AMOUNT OF NITROGEN BROUGHT DOWN BY THE RAIN TO 

 THE SOIL. 



According to Marie-Davy, nitrogeii is added to the soil by the nat- 

 ural meteorological process of rainfall. Nitrogen can exist in water 

 either as a dissolved salt of ammonia or as pure annnonia, or in the 

 state of a nitrate or a nitrite of soda or other alkali, or as com- 

 pounded with carbon, hydrogen, and oxygen, as in the case of organic 

 bodies floating in the water. The nitrogen brought down by the rain 

 water is washed out of the atmosphere where it had existed in some 

 one of these forms, and, although the percentage is small, yet the abso- 



(13.3) 



