258 DOMESTICATED ANIMALS AND PLANTS 
possessed, so far as we know, by any other form of life. When 
the student comes to realize, by the study of the fertility problem, 
the difficulty encountered by farmers in getting sufficient nitro- 
gen into the soil for profitable growth of crops, then the real 
value of legumes as the only natural and cheap source of nitrogen 
will be fully appreciated.? 
The nutritive significance of legumes lies in the high nitrogen 
and mineral content of both the grain and the stem. As the 
grasses are notable for their carbon content in the form of either 
starch or oil, so the legumes are remarkable for their nitrogen 
and mineral content, especially the former. The exceeding 
rarity of nitrogen gives it a high value for animal food as well _ 
as for fertility, all of which goes to make the legumes, agricul- 
turally speaking, the most distinctive family of plants ever do- 
mesticated.2 They make an ideal food for growing animals and 
a fair substitute for meat in the diet of man; indeed, wherever 
in the earth man has lived with little or no flesh food he has 
drawn the more heavily upon the seeds of legumes. 
Clover. Under this general name are grouped a variety of 
species more or less closely related. 
1. Trifolium pratense, the common red clover, sometimes 
called purple clover or meadow trefoil, the latter from its three- 
parted leaf. 
1 Nitrogen costs in the markets, in the form of commercial fertilizers, ap- 
proximately fifteen cents a pound everywhere, but can be produced by legumes 
in the proper rotation for next to nothing. 
2 It is sometimes necessary to “ inoculate” for the growth of legumes; that 
is, to apply the proper bacteria. The bacteria are not the same for different 
species of legumes. For example, the clover tubercle will not develop on the 
alfalfa nor that of the pea upon the bean. If the particular species, say alfalfa, 
has never before been grown in a locality, its specific bacteria will likely not 
be present, in which case the tubercles will not form and no nitrogen will be 
taken from the air, such a plant becoming a heavy nitrogen consumer instead 
of a nitrogen producer. Inoculation then becomes necessary, for if the tuber- 
cles do not form, the legume is very exhaustive to land instead of benefiting 
it, and ultimately itself dies of nitrogen starvation. Inoculation is generally 
effected by scattering over the surface a little soil taken from a field in which 
the same legume has grown with well-developed tubercles. One to one anda 
half bushels per acre is sufficient if evenly applied. 
