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UNIVERSITY OF WISCONSIN STUDIES
ascendency and is benefited, and the other in which the bacteria are stronger,
destroying the plant tissue and acting as parasites.
     Further search of the early literature reveals a growing realization
that not
all strains of any species of Rhizobium are alike in ability to benefit the
host plant;
see, for example, the papers of Lawes and Gilbert, 1890 and 1891; Nobbe,
Schmid, Hiltner, and Hotter, 1892a; Nobbe and Hiltner, 1893; and Deherain
and Demoussy, 1900a and b. During this early period some care was taken to
apply this knowledge in the preparation of cultures. As the value of inoculation
                                      TABLE 14
   The effect of various strains of Rhizobium meliloti on the yield and nitrogen
content of alfalfa
                                                           (After Stevens,
1925a)
                       Dry weight*                   Nitrogen
   Total
   Strains        Roots          Tops          Roots          Tops      
 nitrogen*
                  gm.            gm.         per cent        per cent   
   Mg.
     111          6.719         10.621          1.68          2.59      
    387.9
     100         13.165         12.942          1.79          2.65      
    578.6
     106          9.704         11.070          1.66          2.63      
    454.1
     107          6.926          9.813          1.84          2.60      
    382.5
     104          2.942          5.712         2.16           2.61      
    212.5
     102          2.813          6.078         2.22           2.60      
    220.4
     101          3.931          6.596          1.84          2.41      
    230.5
     105          3.685          5.181         2.01           2.24      
    180.2
*30 plants
                                      TABLE 15
                 The effect of various strains of Rhizobium japonicum on
the
                            yield and nitrogen content of soybeans*
                                                            (After Wright,
1925b)
             Wisconsin Black                Ito San                   Manchu
             Dry         Nitrogen       Dry       Nitrogen       Dry    
  Nitrogen
  Strains    weight        fixed       weight       fixed       weight  
    fixed
               gm.          gm.          gin.        gm.          gm.   
     gm.
    1          815         12.84         894        14.07         853   
    15.91
    2          965         21.51         961        16.86         886   
    11.41
    3          873         16.08         871        13.46         834   
    13.33
    4          788         15.07         888        15.40         861   
    15.31
    5          598          7.05         659         4.48         765   
     7.04
    6          734          9.54         731         5.07         622   
     4.87
*Three-year average of field results. 50 plants in each case.
became better known and the practice more extensively followed, this fact
seems
to have been disregarded and did not again come into prominence until the
work of Stevens, 1925a, with Rh. meliloti and of Wright, 1925a and b, with
Rh.
japonicum.    By carefully controlled and extensive studies, these investigators
demonstrated conclusively that different strains of rhizobia vary in ability
to aid
plant growth. The accompanying Tables 14 and 15 from Stevens, 1925a, and
Wright, 1925b, illustrate the differences existing between strains of a species.
   These studies were followed by other comprehensive studies with strains
of
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