the Progress of English Agriculture, 823 = .5.57 
oducts, is, in a purely practical sense, the most important ele- 
ent with which the farmer has to deal. Hence the great value 
the laborious and long-continued field-experiments by Messrs. 
iwes and Gilbert, and their extremely interesting laboratory 
searches relating to the sources and assimilation of nitrogen by 
ants, and to the exhaustion or accumulation of the same 
™ents in the land. 
What, then, are the sources of the nitrogen of vegetation ? Are Sources of 
ey the same for all descriptions of plants ? Are they to be nitrogen in 
ught entirely in the soil, or entirely in the atmosphere, or ^'^S'^'''*'"" 
rtly in the one, and partly in the other ? These are some of 
c questions which Messrs. Lawes and Gilbert have endea- 
ured to solve by a series of investigations extending over a 
liod of above thirty years, and in which these gentlemen are 
11 engaged ; for although their researches have thrown a good 
I al of light on these questions, they involve great difficulties, 
: d a vast field of scientific inquiry is still left open ; and no 
t ubt much laborious work has yet to be accomplished before 
1 ;y can be satisfactorily answered in all their bearings. 
The combined nitrogen coming down from the atmosphere in 
] in, snow, mists, or dew, undoubtedly contributes to the annual 
'?ld of nitrogen in our crops, but it requires no lengthened 
jTument to prove that this source of nitrogen is altogether 
iidequate to meet the requirements of our cultivated crops. 
According to the average results obtained by Messrs. Lawes from the 
: d Gilbert, and by Professor Way, the combined nitrogen, in rain itmosphere. 
{ d minor aqueous deposits, which fall annually at Rothamsted 
ion one acre of land, amounts to 6'46 lb. as ammonia, and "75 
i nitric acid, or a total of 7"21 lb. of combined nitrogen per acre. 
Professor Frankland's more recent determinations are sub- 
J ntially confirmatory of these results. How much of this 
1 rogen is available to the vegetation of a given area we have 
It the means of estimating with any certainty. Numerous 
ilependent determinations, both by Dr. Frankland and myself, 
c the nitric acid in the drainage-water collected from land at 
lithamsted, which had been left unmanured for many years, 
S)w that a considerable amount of nitric acid passes into land- 
ciinage, and render it all but certain that this loss of nitrogen 
Iich exceeds the quantity brought down upon the land in the 
rn and other aqueous deposits. 
With regard to the free nitrogen in the atmosphere, it may Non-ability of 
t stated that an elaborate investigation into this subject, by p'^uts to 
Tk T ^-11 , -n 1 r 11 /- 1 ii • assimilate free 
J^ssrs. Lawes, Gilbert, and Pugh, fully confirmed the previous nitrosron from 
eWiments made by M. Boussingault, which showed that plants, the air. 
t their leaves, do not appear to have the power to take up and 
a'imilate the free nitrogen of the air. 
