442 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON 
are the sources of all the Nitrogen of our crops beyond that which is directly supplied 
to the soil by artificial means? This brings us to a consideration of the next Section 
of our subject. 
Sxctron II].—_GENERAL VIEW OF THE VARIOUS ACTUAL OR POSSIBLE SOURCES 
OF THE NITROGEN OF OUR CROPS. 
The following actual or possible sources of the Nitrogen obtained in our crops, beyond 
that supplied in manure, may be enumerated :— 
1. The Nitrogen in certain constituent minerals of the soil, especially the ferruginous 
and aluminous; and certain nitrides. 
2. The combined Nitrogen annually coming down in the aqueous depositions from the 
atmosphere :— 
(a) As ammonia. 
(6) As nitric acid. 
(c) As organic corpuscles, &c. 
3. The accumulation by the soil of combined Nitrogen from the atmosphere :— 
(a) By surface absorption aided by moisture. 
(2) By the chemical action of certain mineral constituents of the soil. 
(c) By the chemical action of certain organic compounds in the soil. 
4, The formation of ammonia in the soil, from free Nitrogen, and nascent Hydrogen 
(the so-formed ammonia either remaining as such, or being oxidated into nitric acid). 
5. The formation of nitric acid from free Nitrogen :— 
(a) By electric action. 
(6) With common Oxygen, in contact with porous and alkaline substances. 
(c) Under the influence of Ozone, or nascent Oxygen. 
6. The direct absorption of combined Nitrogen from the atmosphere, by plants them- 
selves. 
7. The assimilation of free Nitrogen by plants. 
A careful consideration of the above actual or possible sources of the Nitrogen of the 
vegetation which covers the earth’s surface will show, in regard to some of them, that 
they at least are quantitatively inadequate to supply the amounts of Nitrogen which 
direct experiment has shown to be removable in various crops from a given area of land. 
(1) The combined Nitrogen that may be due to certain of the constituent minerals of 
the débris of which our soils are made up cannot be supposed to be an adequate source 
of the nitrogen annually carried off in the vegetable produce of the land. 
(2) The combined Nitrogen which comes down from the atmosphere in the various 
aqueous deposits of rain, hail, snow, mists, fog, and dew—whether it be merely the 
return from previously existing generations of plants or animals elsewhere, or whether 
in part the product of a new formation—undoubtedly does contribute materially to the 
