JUNE 28, 1912] 
recognized very early, though nitrogen was 
first recognized as a distinct element in 1772 
by Rutherford. 
Later it was demonstrated that nitrogen is 
an element indispensable to life, present in all 
organisms and the mass of literature, scien- 
tific, popular and commercial, concerning 
nitrogen im its various forms and their rela- 
tion to plant growth is overwhelming to the 
student. 
Yet, notwithstanding the long period of 
time during which we have recognized the im- 
portance of nitrogen, the aggregate of many 
life times that have been devoted to its study 
or the thousands of pages that have been pub- 
lished concerning its relation to plants, there 
still remain some of the most fundamental 
questions for solution. 
The universality of nitrogen in plants is 
well authenticated. The amounts removed 
from the soil by a few leading crops are as fol- 
lows: 
Corn (45 bushels per acre) .... 63 Ibs. 
Cabbage (15 tons per acre) .... 100 lbs. 
Clover hay (2 tons per acre) .. 82 lbs. 
Wheat (15 bushels per acre) ... 31 Ihs., ete. 
Not only is it present, but it is indispen- 
sable, as has been repeatedly shown by careful 
water- or sand-culture experiments. Just how 
and why nitrogen is essential is a much more 
difficult question. It is a necessary element in 
the composition of protoplasm, and many other 
organic substances. It aids in the assimilation 
of other needed elements, and in photosynthe- 
sis. These functions of nitrogen would ac- 
count for the need of a certain amount of 
available nitrogen in soils used for crop pro- 
duction. But it is found that soils with ap- 
parently an abundance of available nitrogen 
for the supply of many crops are benefited by 
the addition of still more nitrogen. Various 
theories which we will not enter upon here 
further than to point out that nitrogen or its 
compounds may serve other uses than by be- 
ing merely absorbed or absorbed and assimi- 
lated have been proposed to explain this pecu- 
liar fact. What these other uses are is one of 
the large questions, as yet barely disclosed. 
SCIENCE 
997 
Whatever other uses nitrogen may serve, that 
of a food element is unquestionably a preemi- 
nent one, and it is with this phase of the nitro- 
gen subject alone that I shall deal. 
Admitting the importance of nitrogen in 
assimilation the next question is: “In what 
forms is nitrogen available to the plant?” 
This, as has been the fate of many questions 
in biology, received its emphatic answer years 
ago, an answer that asserts itself convincingly 
through thousands of popular and scientific 
articles and text-books, but one which seems 
to be founded on very insecure evidence and 
one which is likely to be largely modified as 
research progresses. 
The popular, almost the universal concep- 
tion of available nitrogen is expressed in some 
such words as these, which are taken from 
prominent texts by famous authors and mostly 
from recent works. 
The majority of farm crops can use only that 
part of the nitrogen in the soil that is present as 
nitrate* 
and on a later page: 
The plant can make use of the nitrogen only in 
the form of nitrates. 
The nitrates are the chief source of the nitrogen 
supply of green plants.? 
Sulphate of ammonia . . . must be nitrified be- 
fore the nitrogen is available to plants.® 
The conversion of the ammonia formed during 
the process of putrefaction into the nitrates is a 
matter of greatest importance in soil fertility. ... 
A soil to encourage nitrification must, then, have 
suitable basis. The question of soil fertility is, 
then, in its last analysis a bacteriological problem.‘ 
This conception of nitrates has inevitably 
focused attention on nitrates as a soil factor 
of preeminent, of indispensable importance. 
It makes them appear so valuable that their 
coming and going are of superlative import 
and their failure to attend to spell disaster. 
The subject assigned to me is “ Nitrates in 
1 Vivian, 1909. 
* Bergen and Davis, ‘‘Principles of Botany,’’ 
pp. 233. 
* Percival’s ‘‘ Agricultural Bacteriology,’’ p. 142. 
‘Frost and MacCampbhell, ‘‘General Bacteriol- 
ogy,’’ 1910, p. 288. 
