40 PLANT LIFE IN OKLAHOMA. 



usually found on and about them and some of these are mostly not found 

 elsewhere. 



The most exclusively gypsum hill species are plains pailostrophe 

 (Psilostrophe villosa), and phacolia (Phacelia intergrifolia,) and few- 

 eeeded mentzelia (Mentzelia oligosperma) which grow on the top of the 

 gypsum cap or the last species in clefts in it; Nama (Nama compactum) 

 eeems to be confined almost exclusively to the guttered and weathered 

 sides of these hills, the type locality of the species being the 

 side of the butte in Major County known as Glogs Mountain. The 

 sharp^scaled grass (Erionewon pilosum) is common on somewhat 

 more permanent places on the sides of the bluffs and is seen growing 

 at the mouth of the cave in the illustration (PI. XXI). Evening primrose 

 {Oenothera missown'ensit) , sensitive brier (Mimosa borealis). aster 

 (Aster aricaef alius) , evening primrose (Oenothera Hartwegi var. 

 lavendulaefolia) , hairy purslane (Portulaca polisa), vetch (Astragalus 

 parviflorus) , and (A. cuspidata) are found about the sides and bases of 

 the hills, but they also occur in other locations having red clay soil with 

 a large content of calciujn sulphate. The wild gooseberry (Ribes aurea), 

 ill-scented sumac (Rhus canadensis var. trilobata), and red cedar (Juni- 

 perus virginiana) are often found rooting in the clefts of the gypsum cap, 

 but are as often found in soil not especially rich in gypsum. 



SAND-HILLS REGION. 



Beginning about the middle of the State or a little farther westward 

 there extends a strip of sandy country along the north side of each of four 

 nearly parallel rivers, the Salt Fork of the Arkansas, Cimarron, North 

 Canadian, and South Canadian (PI. VII). These areas are from 2 to 18 

 miles broad and stretch northwestrly 50 to 310 miles. Fear the western 

 edge of the State the sandy area along the South Canadian broadens and 

 becomes continuous on the north with that of Wolf Creek, a tributary of 

 the North Canadian, and extending southward continues to Washita 

 Eiver. Farther southward along the western edge of the State extensive 

 sandy regions are encountered on both sides of Salt Fork and North 

 Pork of Eed Eiver, and east of the latter near its Junction with Eed River. 



The sandy regions along the rivers in the northwestern part of the 

 State seem to owe their origin to certain weather conditions which have 

 maintained for a long period in the past, and to some extent are still 

 operating. • 



These rivers are relatively long, the Cimarron and South Canadian 

 having their sources in the Eocky Mountains. The rains in a semi-ari-d 

 country are usually more rapid and of shorter duration than in better 

 watered regions. In western Oklahoma formerly many rains lasted from 

 15 minutes to an hour, precipitating in that time from 1 to 4 inches of 

 water. The uncultivated condition of the soil and the short duration 

 of the rain resulted in most of the water running off and leaving, it is 



