Bacteriophage 223 



Inoculation of loguminous plants increases the protein content of 

 the plant, olten without increasing the crop yield. Plants that de- 

 pend largel)' upon the bacteria for their nitrogen show a high alka- 

 loid content. When the plants obtain their nitrogen from inorganic 

 compounds, they are poor in alkaloids. This is especially true of 

 lupines. 



Molybdenum is said to have an important effect on nitrogen fixa- 

 tion by leguminous plants. This subject was investigated recently in 

 detail by Jensen, who concluded that nitrogen fixation by alfalfa 

 and white clover in agar culture is not stimulated by additions of 

 molybdenum in quantities exceeding 0.03-0.05 y per plant. As much 

 as 37,000 parts of nitrogen could be fixed per part of molybdenum 

 present. A relatively small but significant response was found to 

 1 part of moKbdenum per 80,000 parts of nitrogen fixed. At a ratio 

 of molybdenum to nitrogen of 1:20,000, further addition of mo- 

 Kbdenum had no effect. The root nodules of leguminous plants 

 grown at low molybdenum concentration contained 5-15 times more 

 molybdenum than did the roots, and the latter were richer in mo- 

 Kbdenum than the tops. Alfalfa plants took up more molybdenum 

 when fixing free nitrogen than when utilizing combined nitrogen. 

 These results suggested that molybdenum stimulates the process of 

 s)mbiotic nitrogen fixation and is undoubtedly required for general 

 metabolism. Vanadium cannot replace molybdenum. 



Bacteriophage 



Root-nodule bacteria are subject to the action of phage, which is 

 quite specific for the different organisms. This phenomenon repre- 

 sents a complicating factor in the host-bacteria relationship. The 

 phage is widely distributed. It has been isolated from nodules, 

 roots, and stems of leguminous plants, as well as from soils in which 

 legumes have grown. Demolon and Dunez found the bacteriophage 

 in the neighborhood of the roots of leguminous plants, but not a few 

 inches away from the roots. As in the case of other phages, resistant 

 strains can easily be obtained. This is complicated by the fact that 

 different phages vary in their ability to cause the lysis of a given 

 sensitive strain. Vandecavaye and Katznelson isolated a phage which 

 caused lysis in a dilution of 10~". According to Demolon and 

 Dunez, phages from clovers, lupine, and pea are able to lyse prefer- 

 entially the particular species of bacteria, but some phages seem to 

 be more general in their effectiveness upon different strains of rhi- 



