BY K. GKEIG SMITH. 671 



common with all yeasts the i-hizobia under certain unfavourable 

 conditions, and notably within the nodule, may grow to long and 

 irregular forms, just as some of the most pronounced saccharo- 

 mycetes grow as sausage-shaped and lengthened forms. With the 

 latter this frequently occurs when they are grown on solid media, 

 and also when cultivated for a long time on the surface of ]i({uid 

 media. 



When young cultures of Rkizohium are placed upon the gypsum 

 block, as is customary in determining ascospore formation with 

 the yeasts, and maintai)ied for a few iX&ya at 22° C, the proto- 

 plasm of the cell is seen to aggregate into points and finally 

 disappear, the cell meanwhile swelling and losing its staining 

 power. Among the cells occur a number of coccus forms, but 

 since they occur free, and liave not with certainty been seen 

 inside the cells, they are probably Ijuds and not ascospores. 

 The older cultures on gypsum show only a collection of non- 

 staining forms. 



Experiments were made with pure cultures of the organism, 

 using glucose and sucrose in conjunction with plant extract, but 

 neither with Rhizohia obtained from the lupin nor the pea could 

 any fixation of free nitrogen be found either in faintly acid, 

 neutral or faintly alkaline media; the cultures finally contained 

 the same amount of nitrogen as they liafl at the beginning of the 

 experiment. 



Witli regard to the other (organisms oi the nodule, examination 

 of the crushed nodule suspension shows what is virtually a pure 

 cultiu-e of Rkizobium. Other organisms are so few in number 

 that they are o^•erwhelmed by the nodule formers. So numerous 

 are they that an}^ doubt as to whether other organisms may cause 

 the formation of the nodule is at once dispelled, and Rhizobiani 

 undoubtedly plays the chief if not the only role. Other organisms 

 do occur, Init most of them may be looked upon as accidental, 

 since thej^ are not universally found in all nodules. There is one 

 organism, liowever, which has lieen found very frequently in the 

 nodules of peas, lupins and vetches. It grew so freely upon 



