Chapter VIII. 
RELATION OF PLANTS TO ATMOSPHERIC NITROGEN. 
IN GENERAL. 
If the atmosphere varied largely in its chemical constituents. this 
would 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 shght, systematic variation in the proportions 
of nitrogen and oxygen. But all these variations are so small as 
compared with the variations in the quantity of air brought to the 
plants 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 Marié-Davy, nitrogen 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 ammonia, 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- 
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