NATIVE LEGUMES OF NEBRASKA AND KANSAS. 7 



FACTORS INFLUENCING THE DISTRIBUTION OF WILD LEGUMES. 



The distribution and abundance of legumes are influenced by many 

 factors, one of the most marked of which is the adaptabiHty of the 

 locahty for the production of heavy crops of grass. Few legumes can 

 compete with a thrifty growth of grass. Where Andropogonfurcatus 

 (bluestem) luxuriates, few legumes except Psoralea seem to be able to 

 persist. 



On the densest swards of Bulhilis dactyloides (buffalo grass), Vicia, 

 Psoralea, Lotus, and Astragalus are occasional habitants, but none of 

 them are able to constitute a very large proportion of the plant growth. 

 On poor soils and slopes where the grass is thin, both the number of 

 individuals and the number of species of leguminous plants are usually 

 greater than on rich soils and level tracts, and legumes consequently 

 form a very much larger proportion of the flora. But on all soils and 

 in all climates of the region legumes peculiarly adapted to the condi- 

 tions are present in large numbers. 



In many of the meadows in the river valleys of Iowa, South Dakota, 

 and northeastern Nebraska, Crotolaria sagittalis covers most of the 

 ground. On level sand beds near streams Acuan grows in profusion, 

 and on thinly grassed sandy bottoms Cassia chamaecrista (partridge 

 pea) is often abundant. On many low sand hills Psoralea is almost 

 the only habitant, while on the tops of sand hills where there is little 

 vegetation Phaca longifolia is preparing the way for more plant growth 

 and is often assisted in this work by Kuhnistera villosa and several 

 other species. 



LEGUMES ARE CROWDED OUT ON THE RICHEST SOILS. 



It does not seem that most of these legumes choose the poorer soils, 

 for, in fact, many of them grow much better on rich soil, but when the 

 soil becomes rich in nitrogen and humus other plants which do not 

 thrive on poor soil are able to crowd out the legumes. There is good 

 reason to believe that lands that are now richest formerly supported 

 the densest leguminous growths, except, perhaps, where the fertility 

 has been washed down from higher levels. 



NUMBER OF GENERA AND SPECIES IN DIFFERENT LOCALITIES. 



While the number and distribution of individuals on arable lands, 

 and not the number and distribution of genera and species in the State, 

 is the important factor for our purpose, yet this latter question de- 

 serves mention. Pound and Clements^ give 23 genera and 103 species 

 of legumes as occurring in Nebraska. There are 23 of the species 

 characterized as inhabitants of low prairies and meadows, which con- 

 stitute most of the farm lands, 36 of high prairies, sandy bluffs, and 



a Phytogeography of Nebraska, p. 240. 

 [Cir. 31] 



