154 
this is the generally accepted view to-day. The organisms do not 
act like ordinary bacteria, since they grow in a different way and 
have a somewhat different form. It is a matter of comparatively 
little importance, however, whether the organisms are regarded as 
true bacteria or simply as related organisms. The significant fact 
is that they are colorless microscopic organisms, living in the soil, 
belonging to the low fungi and having the remarkable functions 
above pointed out. 
The work of the last two years has shown further that there 
are a number of different species of these root organisms and that 
different species of legumes are associated with different species 
of these bacteroids. The organism which produces the root tu- 
bercles of the lupine will not produce the root tubercle of the pea, 
and, although the subject has not been as yet very thoroughly 
cleared up or studied very widely, it seems that nearly all of the 
different species of legumes are associated with different forms of 
organisms in the soil. It has followed from this that special soils 
are especially adapted for the growth of certain species of legumes. 
A soil for instance in which the lupine has been growing is much 
better adapted for the production of tubercles on lupine roots 
than it is for the production of tubercles on the roots of the pea, 
simply because the soil is already filled with the organisms which 
can grow in the lupine and not yet provided with that growing in 
the pea. It requires thus a culture of a year or two to develop in 
the soil a sufficient quantity of the appropriate species of bacteria 
to render the growth of any species of legume especially advan- 
tageous. The special work of bacteriologists at the present time 
is turned largely in the\direction of determining the facts in re- 
gard to this matter of bacteria species associated with the different 
species of legumes. 
It is plain from the above that the production of root tubercles 
is not a normal feature of the life of the pea plant, and that the bac- 
teria have some peculiar relation to the higher organism. It is, 
however, hardly proper to regard their relation as that of a parasite 
and its host. It is true that the bacteria grow in the root of the 
legume and doubtless obtain sustenance therefrom, but the higher 
organism does not suffer from the parasitism and the relation of: @ 
_the two organisms is rather that which is known as symbiosis,i.€2 
