96 
Journal oj Agricultural Research 
Vol. XXX, No. 1 
Table II .—Effect upon nodulation of 
increasing the number of bacteria 
Tumbler No. 
Number 
of or¬ 
ganisms 
applied 
per seed 
Plants 
inocu¬ 
lated 
Number 
of 
nodules 
per 10 
plants 
1 A_ 
0 
Per cent 
0 
0 
IB__ 
0 
0 
0 
1 C_ 
0 
0 
0 
2A_ 
1 
0 
0 
2B_ 
1 
0 
0 
2 C_ 
1 
0 
0 
3A_ 
10 
1 
3 
3B__ 
10 
1 
5 
3C__ 
10 
1 
4 
4 A_ 
25 
100 
48 
4B_ 
25 
100 
62 
4C_ 
25 
100 
51 
5 A__ 
50 
100 
60 
5B__ 
50 
100 
68 
5C_ 
50 
100 
71 
6 A.. 
100 
100 
59 
6 B_ 
100 
100 
66 
6 C__ 
100 
100 
73 
7 A_ 
500 
100 
65 
7B____ 
500 
100 
78 
7C.... 
500 
100 
63 
Both tables show that a high number 
of infecting organisms will not give a 
better inoculation than a moderate 
number. Theoretically, it seems that 
infection and nodulation are partly a 
hit-or-miss affair. When a limited 
number of nodular organisms are pres¬ 
ent the chances of contact between host 
and bacteria are naturally not so great 
as when a large number of organisms 
are present. Therefore the greater 
the number of infecting organisms the 
greater should be the number of nod¬ 
ules produced. This ratio between 
bacterial numbers and nodulation holds 
only when the number of organisms is 
very limited and approaches infinity as 
the number of bacteria is increased. 
It is therefore apparent that there must 
be a maximum infection obtainable and 
that after this maximum is reached the 
plants become immune to additional 
infection. 
The conclusions to be drawn are: 
1. When the number of nodular organ¬ 
isms is limited there is a distinct rela¬ 
tion between the number of organisms 
present and the number of nodules 
formed. 
2. There is a rather definite minimum 
number of nodular organisms required 
to produce maximum infection. 
3. After a certain degree of infection 
is reached the host is immune to addi¬ 
tional infection. 
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