14 

 Source of Cultures Distributed. 



The cultures which we have sent out to Canadian farmers have been 

 isolated and cultivated in this laboratory, and each culture was from its 

 appropriate host plant. Thus, the alfalfa culture was isolated from a 

 nodule on the root of an alfalfa plant, the vetch culture from the vetch 

 nodule, and so for the red clover, white clover, pea, field bean, etc. 



When a pure culture was once obtained it was transplanted at inter- 

 vals and a record of each transplantation was kept, so that each mother 

 culture, and therefore each culture which we sent out, can be traced back 

 to its original nodule. 



The cultures were isolated in the spring- and summer of 1904, and 

 had, therefore, been grown on artificial media from two years and a half 

 to nearly three years, and in that time had been transplanted several 

 times. The longest period between two successive transplantations was 

 in some cases more than a year. 



Fig. 12. — Colony on agar of nodule- 

 bacteria from Alfalfa Root. Mag- 

 nified 200 diameters . 



Fig. 13. — Colony of nodule-forming 

 bacteria from Flat Pea. Magni- 

 fied 100 diameters. 



In preparing the culture media, we took pains to exclude combined 

 nitrogen, and the media was all nitrogen poor. Five of the eight cultures 

 were proved, that is, they formed nodules on the roots of their appropriate 

 host plants in the absence of all other bacteria. 



During the spring of 1908, cultures of the nodule-forming bacteria 

 will again be distributed from this laboratory to Canadian farmers upon 

 receipt of twenty-five cents for each culture, which is sufficient to treat 

 sixty pounds of seed. It is expected further that the recipients of the 

 cultures will report the results of his experiment, sowing some uninocu- 

 lated seed for comparison. 



Those who intend to use the culture should read what follows: 



These bacteria under natural conditions combine the free nitrogen 

 of the air only in association with plants of the bean family. Therefore it 



