ORIGIN OF THE CULTIVATED LEGUMES 26 1 



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. 1 



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. 2 



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 



