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, 

 winch 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 



