PLANT FOOD 17 
soil. These fall into four chief groups—decomposers, 
nitrifiers, denitrifiers, and nitrogen-fixers, and they 
have: been investigated mainly from the point of view 
of the total balance of nitrogen which they maintain in 
the soil. Recent research, however, has shown that at 
least equal importance attaches to certain intermediate 
products formed by the decomposition bacteria which 
not only influence the activities of other soil bacteria, 
but also act directly upon plants growing in the soil. 
For some years past an investigation into the nature 
and composition of the organic matter of the soil from 
the standpoint of biochemistry has been in progress 
by the scientific staff of the Bureau of Soils department 
of the United States Department of Agriculture. The 
results already obtained have thrown considerable 
additional light upom the question of soil fertility. 
For example, Schreiner and Skinner have shown that 
certain decomposition products of nucleo-proteins and 
proteins, such as xanthine, guanine, creatinine, histidine 
and auginine, which they have isolated from fertile soils, 
can replace nitrates in a water culture solution and are 
directly used in building up plant protein. This dis- 
covery that beneficial organic decomposition compounds 
exist in soils and play a prominent part in the life 
processes of growing plants is of fundamental importance 
in soil fertility. 
The significance of the organic constituents of the 
soil has not received the attention it deserves in this 
country, and it is unfortunate that this promising field 
of research has not attracted more workers. 
For the last few years research has been in progress in 
the Botanical Department of King’s College, London, 
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