42 PLANT IJFE IN OKi.AHOMA. 



The soils of the State may be f:^rouped under the following heads: (1) 

 Eesidual soils; (2) Transportcnl soils. Under the second type are: (a) 

 Colluvial soils; (b) Alluvial soils; (c) Aeolian soils. Eesidual soils are 

 those which have been formed in the place where they are now found, 

 and the soils of Oklahoma belong chiefly to this type. The transported 

 soils of the State consist of those along the streams and the sand areas 

 of the State. The eastern half of the State has limestone generally present 

 in the soil. The western half has an abundance, and even an excess of 

 gypsum, even in the sand hill areas which are in the general gypsum 

 region. The ground water also contains gypsujn, and wells in the Per- 

 mian red clay often furnish water so strong with gypsum that farmers 

 must depend upon cisterns for holding water for domestic purposes. A 

 large percentage of the soils of the State are alkaline. The percentage of 

 acid soils is relatively small. 



PRECIPITATION. 



The rainfall is greatest in the southeastern part of the State, where 

 it averages aibout 43 inches per year, gradually diminishing westward to 

 Cimarron County, where the average is only 15 inches per year. A con- 

 siderable part of the central-western part of the State also has a scanty 

 rainfall. For further information concerning the precipitation, the reader 

 is referred to a discussion of rainfall on page 37. 



Lines marking places of equal rainfall extend mostly a Little west of 

 south from the northern boundary of the State. 



LIFE ZONES. 



Four life zones have been distinguished in Oklahoma. The 

 Upper Austral covers a small area at the middle of the north edge 

 and most of the Panhandle. The Carolinian zone extends over the 

 rough and elevated regions in the eastern part of the State. The Lower 

 Austral zone covers the central and a part of the eastern portions, while 

 about two-thirds of the eastern portion is in the Austroriparian. These 

 regions pass imperceptibly into each other, except in a few cases, where 

 the change is rather abrupt (the Carolinian having rather distinct lines 

 of contact with the Austroriparian) . 



RELATION OF PHYSICAL CONDITIONS TO THE FLORA. 



In Oklahoma the problem of determining the relation of the different 

 types of soil, of the elevation (life zones),, of rainfall, and of distributing 

 agents to the distribution of our species is complicated and difficult. By 

 reference to the maps contained in this report, it will be seen that the 

 lines showing the limits of the geological formations, and lines of equal 

 rainfall largely coincide, and that the lines of equal elevation also in a 

 general way coincide with these. Along the line of junction between the 

 Pennsylvanian and Permian formations, numerous species reach the limit 

 of their western range in the State. Conspicuous among these are Syca- 



