16 FORAGE PLANTS AND THEIR CULTURE 



white clover, are indifferent to lime. A few, like lupines 

 and serradella, are injuriously affected if lime be added 

 to the soil. Perennial legumes have as a rule stout roots 

 which serve partly as storage organs for reserve food. 

 Partly on this account, they are cut for hay in early bloom, 

 as after this stage reserve stuff is deposited in the roots. 



10. Root nodules. On the roots of most legumes and 

 a few other plants occur nodules or tubercles. Woronin 

 in 1866 discovered that these contained bacteria-like 

 organisms, but their importance was not realized until 

 Hellriegel in 1887 demonstrated that leguminous plants 

 can utilize atmospheric nitrogen by the aid of these 

 nodule bacteria. When the root nodules are absent, 

 legumes, like most other plants, must depend on com- 

 bined nitrogen in the soil. 



It was known to the Romans in Pliny's time that 

 certain legumes helped succeeding crops, and indeed 

 legumes mixed or in rotation with other crops have been 

 used in India and China probably since prehistoric times. 

 The importance of leguminous crops is, however, more 

 clearly recognized since their role as nitrogen conservors 

 has been discovered. 



11. The nodule organism. The organism causing the 

 nodules in legumes is now called Pseudomonas radicicola. 

 Apparently it is but one and the same species that causes 

 the nodules on legumes and on such plants as Alnus, 

 Shepherdia, Podocarpus, Ceanothus and others. The 

 organism occurs in different physiological forms, for it is 

 not possible, except in a few cases, to inoculate a legume 

 of one genus directly with the nodule bacteria from another. 

 The only definitely proved case of this is Melilotus and 

 Medicago-, alfalfa being readily inoculated by sweet clover. 

 It is probable, also, that the bacteria of garden peas in- 



