248 FIELD CROP PRODUCTION 



247. Bacteria in relation to different legumes. Since 

 the bacteria may enter any of the root hairs, there is no 

 uniformity in the arrangement of the nodules on the roots. 

 There are, however, characteristic shapes of nodules for 

 the various species of legumes. This is due to the fact 

 that each species has a slightly different kind of root 

 development, and, when penetrated by bacteria, they 

 produce distinguishing types of nodules. It may be due 

 also in part to the fact that the same kinds of bacteria do 

 not work on all kinds of leguminous plants, but that each 

 species enters into partnership with a special variety of 

 bacteria. Thus we have the red clover variety of bac- 

 teria, the soy bean variety, etc. The bacteria that form 

 the nodules on the roots of red clover will not grow on 

 the roots of the soy bean, and vice versa. Sometimes, 

 however, one variety of bacteria may form nodules on 

 two or more species of legumes; thus the same bacteria 

 will grow equally well on the roots of alfalfa, sweet clover, 

 and bur clover. It is probable that the various kinds of 

 leguminous bacteria are not distinct species, but varieties 

 of Bacillus radicicola. 



248. Adaptation and distribution of bacteria. Cer- 

 tain conditions of the soil seem to retard the growth, and 

 in some cases completely prevent the activities of the 

 leguminous bacteria. The different varieties of bacteria 

 of course have widely differing adaptations, but almost 

 all varieties are sensitive to acid soils. While the variety 

 that grows on the roots of alsike clover may grow in acid 

 soils, they grow much better in soils well supplied with 

 lime. The variety that grows on the roots of alfalfa and 

 almost all other cultivated legumes is almost dormant 

 in acid soils. Neither do they thrive in wet soils, and 

 frequently drainage is necessary to secure their services 



