ORIGIN OF THE CULTIVATED LEGUMES 261 
cuttings whose total weight ranges from four to as high as five 
or six tons per acre. 
We know now that the early failures of this plant were due 
not to clay subsoils but to the absence of its characteristic bac- 
terium, without which it could not draw upon the free nitrogen 
of the air; thus it was thrown, like other crops, back upon the 
supply contained within the soil, which is insufficient, except in 
rare cases, to afford material for so heavy a feeder as this crop.! 
This reason for its failure in the eastern states is supported 
by the fact that a few individual plants always succeeded. These 
were the ones that sprang from seeds which happened to have 
had a little of the inoculation from the soil in which the crop had 
been growing. Alfalfa, however, is a ‘‘ clean-seeded crop.”” But 
little seed is sown, and it would take many years to establish so 
vigorous a feeder by the natural means of infection. The eastern 
farmers gave it up too soon. The Kansas people persisted till 
they succeeded, though it took a generation. Fortunately for 
Illinois and the upper Mississippi valley, when the attempt was 
made there Dr. Hopkins of the University of Illinois succeeded 
in showing that the question of success or failure turned upon 
the presence or absence of the characteristic bacteria. After 
having conclusively shown this, he secured a ton of soil from 
an old alfalfa field in Kansas. With this he thoroughly inocu- 
lated an acre of the university farm, and from this all Illinois 
and much neighboring territory have been inoculated and the 
culture of this wonderful plant successfully introduced for the 
first time in the Middle West without the usual and otherwise 
necessary delay of waiting for the slow inoculation from seed 
and the long-continued failures necessarily involved. 
1 Alfalfa growing without inoculation is, of course, a nitrogen consumer, and 
as it lives for seven or eight years it will, long before that time, exhaust the 
nitrogen of most soils and die of starvation. 
2 Curiously enough it was learned that wherever the closely related plant, 
Melilotus alba, or sweet clover, grew wild no inoculation was necessary, and 
later it was discovered that soil taken from a sweet-clover spot would success- 
fully inoculate for alfalfa, the first and only instance known in which the bac- 
teria of one species will grow upon another. Whether the bacteria are identical 
