INOCULATION FOR LEGUMES 169 
that this peculiar function may be exercised, it is 
necessary that there shall be present in the soil 
certain organisms which attach themselves to the 
roots of the plants. The presence of these organ- 
isms is indicated by the formation of tubercles or 
nodules on the roots, which range in size on differ- 
ent kinds of plants from that of a pin-head to that 
of a pea. When these nodules are not present, it 
is usually an indication that the proper organisms 
are absent and that the legumes, in common 
with other plants, must derive their nitrogen from 
the soil; and thus, from the standpoint of accu- 
mulation of nitrogen, they are probably no more 
useful than the cereal or other crops. 
Investigations of the life-history of these minute 
organisms show that there are certain conditions 
unfavorable for their growth and development, 
which explains why they are absent in many soils 
For example, it has been shown that they are likely 
not to be present in soils that are poorly drained, 
and when air cannot penetrate and circulate freely. 
It has also been found that an acid-condition of 
soil is not favorable to their growth. They are also 
liable, even if originally present, to be destroyed 
at certain periods if soils are allowed to remain 
uncultivated for some time. In other words, in 
undrained, acid, and light sandy soils deficient in 
organic matter, the organisms are not so likely to 
be present as in those that are well supplied with 
