30 
number are nitrogenous and it is of special interest in this connection 
that- practically all of these have been found to be beneficial to plant 
growth. Certain nonnitrogenous bodies, however, were also isolated, 
one of which, dihydroxystearic acid, seems to have been formed 
under the action of heat and which has been found to be distinctly 
toxic to plants. 1 It has been known for some time that steam heat 
may bring about toxic conditions in soils, apparently of an organic 
nature, but it remained for Schreiner and Lathrop to determine 
definitely what is at least one of the toxic bodies thus produced. 
On the one hand, these authors have shown that definite nitrogen 
compounds of a character beneficial to plant growth are formed by 
the action of heat, while on the other, a toxic compound, also organic 
and definite in character, may be generated at the same time. The 
significance of these discoveries is at once apparent; the value of 
such definite and fundamental data can not fail to be important. 
A knowledge of the effects of steam heat on soil organic matter has 
special bearing on greenhouse practices, but may it not well be asked, 
what are the effects of dry heat without pressure ? This phase of the 
question has not been exhaustively studied. It is unsafe to conclude 
a priori that the same types of cleavage and hydrolysis take place in 
the absence as under the influence of pressure. There is evidence in 
the growth and appearance of crops on burned soil that nitrogen is 
made available by the heat. The deep green color of the crop is 
sometimes very striking. It is important, therefore, that this phase 
of the question be investigated in a general study of soil heating on 
account of the importance of nitrogen in the nutrition of plants. 
In an altogether different connection our attention was drawn to 
the very large increase in the ammonia of some Hawaiian soils brought 
about by the action of heat. It was observed that the ammonia con- 
tent of certain soils increased from a few parts to over 400 parts per 
million. At the same time the nitrates were decomposed. From 
these observations and its general bearing on soil heating, an investi- 
gation of the nitrogen transformations seemed of interest and impor- 
tance. Whence the ammonia thus set free and from what class of 
compound does it arise ? 
The nitrogen of soils having been at one time bound up in organized 
tissue, plant and animal, and, therefore, largely of proteid nature, 
undergoes hydrolysis under the action of enzyms, bacteria, etc., with 
the resulting formation or splitting off of simpler compounds. In 
soils there must occur every stage of these changes from the proteid 
complex, on the one hand, to inorganic compounds, on the other. The 
larger part of soil nitrogen exists, however, in complex organic com- 
binations. Nevertheless, the simple inorganic nitrogen compounds, 
» U. S. Dept. Agr., Bur. Soils Bui. 80 (1911). 
