JUNE 28, 1912] 
least by far the most readily utilized form of 
nitrogen. The vast amount of research car- 
ried on in many laboratories regarding the 
processes of nitrification and dentrification 
indicate that these phenomena are regarded as 
.of high significance and nitrogen of superla- 
tive value. Is this so? 
Nitrogenous organic matter may be classi- 
fied as proteids, albuminoids, amides and alka- 
loids. The larger part of the organic nitrogen 
in soils probably consists of acid-amines and 
amino and amino-acids. 
To what extent may these or their degenera- 
tion products, particularly ammonia, serve as 
plant food? 
A few years ago most special students and 
perhaps all general writers would have said 
that these substances must undergo nitrifica- 
tion before they are available to plants. To- 
day, without much evidence, perhaps without 
any evidence that will stand searching criti- 
-cism, there is a tendency among some writers 
to hedge on this point and to speak of am- 
‘monia as well as nitrates as possessing avail- 
able nitrogen. We even hear the term “ active 
nitrogen” embracing ammonia and nitrate 
nitrogen. 
The evidence on this question is too volu- 
‘minous to bring before you, but we may sum- 
marize it something as follows: 
Innumerable experiments have been made 
bearing upon the relative availability of ni- 
trate and ammonia nitrogen to plants. Most 
‘numerous of such have, of course, been field 
tests of ammoniacal compounds and of ni- 
‘trates drawing conclusions from the yield or 
‘the crop analyzed. Such tests are manifestly 
inconclusive, since in all cases the question of 
nitrification in the soil is an ignored factor 
‘and it is not in reality known whether the 
ammonia that is applied to the soils is used 
as such or is first nitrified or indeed whether 
the reverse may not be true, viz., that the ni- 
‘trates have been reduced to ammonia and 
utilized in that form. The general conclusion 
that can be drawn from such experiments is 
+hat ammonia applied to soils does not, with 
most crops, on most soils, give so large crop 
‘returns as do nitrates. The common ratio of 
SCIENCE 
999 
utility is generally given as something like 60 
or 70 to 100. This conclusion varies, however, 
for different crops, different soils, different 
times; and such experiments are far from giv- 
ing a solution of the fundamental question. 
Another line of attack is by means of water- 
culture experiments. Many such lack bac- 
teriological control and the conditions regard- 
ing nitrification are not known. A few have 
been conducted with rigid bacteriological con- 
trol and do actually prove that a plant can 
assimilate ammonia without its previous 
nitrification. Such tests, however, do not 
simulate field conditions much more closely 
than would experiments on the habits of 
squirrels parallel nature if conducted in 
aquaria. Our results of comparative tests of 
the functions of bacteria in soils and in solu- 
tions have given us entire lack of faith in such 
abnormally conditioned experiments. 
Again, plants have been grown in sterile 
soils under aseptic conditions, with constant 
and rigid chemical and bacteriological con- 
trol. Such results may properly pose as 
qualitative. But they are not quantitative, 
because of necessity they are conducted on 
but a few plants and the factor of individual 
variation is so great that quantitative results 
are vitiated unless a sufficiently large number 
of plants be used to reduce the coefficient of 
error to something like a negligible quantity. 
Also the conditions of control involving. ab- 
normal radiation, ventilation, etc., are unsatis- 
factory. 
Jost says: 
Many hundred culture experiments in water and 
sand have established the fact that nitric acid 
forms an excellent, not to say the best possible 
source of nitrogen for the great majority of plants. 
(How the divergent results arrived at by Treboux 
(1905) are to be explained it is, as yet, impossible 
to say.) 
The recent comprehensive researches of Pitsch 
(1887-1896) and of Mazé (1900) have conclu- 
sively proved that the nutritive value of ammonia 
must not be entirely denied; in the majority of 
green plants it is second only to nitric acid in 
value. 
5 Jost’s ‘‘Plant Physiology,’’ pp. 134 and 135. 
