FIXATION OF NITROGEN 127 



which is the vitality of the culture. If it is old and made 

 up of weakened bacteria, good results will not be obtained. 

 The culture must be grown under favorable conditions and 

 be fresh to give good results. It is possible to bring large 

 numbers of the bacteria into intimate contact with the seed 

 by inoculating it directly with the culture. 



The bacteria that will produce the nodules on the roots 

 of one legume will not necessarily do so on a different 

 legume. The legumes may be divided into separate groups 

 within which the bacteria from one legume will produce 

 nodules on the roots of the other legumes in the group, or 

 "cross-inoculate." The following list gathers the common 

 leguminous plants into unmps that cross-inoculate: 



1. To inoculate red clover, use the bacteria from red 

 clover, mammoth red, alsike, crimson, Egyptian, or white 

 clover. 



2. To inoculate alfalfa, use the bacteria from alfalfa, 

 white sweet clover, yellow sweet clover, bur clover, yellow 

 trefoil, or fenugreek. 



3. To inoculate garden pea, use the bacteria from garden 

 pea, field pea, hairy vetch, spring vetch, wild vetch, broad 

 bean, lentil, sweet pea, or perennial pea. 



4. To inoculate cowpca, use the bacteria from cowpea, 

 partridge-pea, peanut. -Japanese clover, velvet bean, lima 

 bean, wild indigo, or tick trefoil. 



f 5. To inoculate garden bean, use the bacteria from gar- 

 \den, field, navy, kidney, or scarlet runner bean. 



6. To inoculate lupine, use the bacteria from lupine, ser- 

 radella, or wild lupine. 



7. To inoculate soybean, use only the bacteria from the 

 soybean. 



The bacteria enter the plant through the root hairs. 

 They stimulate the growth of the cells at the point of en- 

 trance, and the nodule is produced. If this nodule is ex- 



