ARE THERE DIFFERENT SPECIES OF TUBERCLE BACTERIA 109 
nitrogen fixing while green plants do not have such power, the 
probability is in favor of the latter view. However this may be, it 
is certain that the legumes obtain from the growth of the tubercles 
an extra supply of nitrogen which is derived from the air. 
ARE THERE DIFFERENT SPECIES OF TUBERCLE BACTERIA 
It is practically certain that nearly all soils contain bacteria 
capable of living in symbiosis with leguminous plants. Nearly 
all soils, except extremely sandy soils that support little or no 
vegetation, will support leguminous plants and develop tubercles 
on their roots. One can hardly examine the roots of legumes any- 
where without finding tubercles, a fact which shows that the bac- 
teria in question are very widely distributed in nature. But are 
the bacteria all of the same species? A very large number of 
species of legumes with their tubercles can grow in most if not all 
soils. Are the bacteria that form tubercles upon the clover the 
same as those that form them upon the pea, or is there a different 
species of bacteria for the different species of legume? It would 
not seem probable that there could be in the soil a different variety 
of bacteria for every variety of legume, but rather that one kind 
of bacteria can grow in many legumes. But the facts are not 
quite so simple as this. Not all species of legumes are capable of 
developing root tubercles equally well in all soils. Some soils will 
luxuriantly support certain species of beans, peas, or clovers, 
producing a large crop, developing quantities of tubercles and 
fixing an abundance of nitrogen, while the same soil will not 
support other species of legumes with equal readiness. For 
example, the soil of Connecticut is not adapted to the legume 
called the soy bean. When this bean is planted in the ordinary 
Connecticut soil it does not flourish, but yields a small crop unless 
heavily fertilized, and does not produce tubercles. This species 
does, however, grow readily in Massachusetts. Some years ago 
the experiment was tried of importing Massachusetts soil, upon 
which this plant had produced abundant tubercles, and mixing it 
