INTRODUCTION 17 



oculate vetch and vice versa, but this lacks proof, as does 

 Nobbe's contention that Pisum will inoculate Phaseolus. 



12. Forms of root nodules. The root nodules on 

 different legumes vary greatly in size, shape and abun- 

 dance. To a certain extent they are characteristic for 

 each genus. The nodule is morphologically a modified 

 rootlet. In many legumes it is always simple, but in 

 others is more or less branched, sometimes into a coral- 

 like mass. In the common cultivated clovers the nodules 

 on the younger roots are small and globose, becoming 

 club-shaped and often bilobed. On older roots they 

 become more branched or lobed. 



Alfalfa produces nodules much like red clover, but 

 usually longer and more branched. 



On Canada peas and the vetches the nodules are still 

 more branched and fan-shaped in form. Clusters of 

 these often form globose masses. 



In the cowpea, peanut and most beans, the nodules 

 are irregularly globose and solid. These are frequently 

 as large as a pea seed. On the soybean, the nodules are 

 also globose but marked on the surface with raised ridges. 



The velvet bean produces perhaps the largest nodules 

 of any legume. These are sometimes as large as a base- 

 ball. Such are really clusters of branched nodules but 

 packed together very densely. 



13. Natural inoculation. Any legumes may easily 

 be inoculated on new land by scattering soil from an old 

 field where the same legume has previously produced 

 nodules, as is nearly always the case when a legume crop 

 is successful. This method was used in Europe before 

 its significance was discovered. In thus inoculating new 

 land, from 100 to 500 pounds of old soil should be used 

 to the acre. It may be scattered in any convenient way, 



