THE AMERICAN BOTANIST. 
75 
in return for a habitation on their roots provide them 
with nitrogen which they are able to obtain from the air. 
Although all ordinary plants require nitrogen, the\^ are 
unable to secure it from the air w^ithout the aid of bacteria 
and the partnerships which clovers have formed are very 
much to their advantage. Until a comparatively recent 
period little attention has been paid to these minute 
plants, but renewed study indicates that possibly a 
majority of the leguminous plants have their own species 
of bacteria and will not thrive with any other. It has 
long been known that in some of the States of the Middle 
West the red clover ordinarily will not grow in certain 
soils and it is only lately that it has been ascertained that 
this is because its favorite bacteria are missing. Know- 
ing this, all the farmer has to do to get a good crop is to 
obtain some soil from an old clover field and inoculate his 
soil with it. Thereafter he may raise clover as long as he 
pleases, but should he raise other crops on the land for 
half a dozen 3^ears in succession, the bacteria will die out 
and the field must be inoculated again before he can raise 
another clover crop. Other legumes are not so particular 
and in most cases either have sufficient bacteria attached 
to their seeds to enable them to get a start or they find 
the right bacteria in the soil, possibly the kind that affects 
some native plant. The alfalfa is another of the species 
that is a bit particular about its bacteria and so will not 
grow in every soil. It is interesting to know, however, 
that the common sweet clover is partial to the same 
species of bacteria, and that wherever sweet clover grows 
there will alfalfa grow, also. Fields in which sweet clover 
is not found may be inoculated with soil from a sweet 
clover patch and then will produce abundant crops of 
alfalfa. In this case both the clover and alfalfa are 
imported plants and the bacteria seems to have been 
imported with them but while the sweet clover is able to 
look out for itself and spreads rapidly, alfalfa is slower to 
take possession of new soil. Possibly the clover seed 
offers a better opportunity for the lodgement of bacteria. 
