44 PLANT LIFE IN OKLAHOMA. 



and into the Transition or Alleghanian; and (h) species wliose northern 

 range limits lie in the Upper Austral or Carolinian. (2) Mid^Miisissippi 

 Valley flora, species ranging well into both the Upper Austral or Caro- 

 linian and the Lower Austral or Austroriparian. (3) Southern flora, 

 consisting of species whose ranges are confined to the Lower Austral and 

 Austroriparian, and divided into two groups: (a) those species ranging 

 mostly through the lower Mississippi Valley, and (b), those species 

 having ranges confined to Oklahoma, eastern Texas, and Louisiana. (4) 

 Western species placed into two groups: (a) those whose ranges extend 

 westward beyond the Upper Austral and into various zones 'beyond, and 

 (b) those species confined to the Upper Austral zone (Great Plains). 

 (5) Local species: (a) those species whose ranges do not extend beyond 

 any adjacent state, and (b) those whose ranges are confined to Oklahoma. 

 There is some duplication of species in division (3) group (b), and 

 division (5) group (a), but the number is less than one per cent. 



Approximately 5 per cent of our species are found throughout the 

 State, or in other words, 19 out of 30 of oux plants reach the limit of 

 their ranges in Oklahoma. 70 per cent of our flora is the western ex- 

 tension of Mississippi Valley flora, and 7 per cent more is doubtless 

 derived from the flora of that region. Twenty-one per cent is derived from 

 the Great Plains or more westerly regions, and there are reasons for 

 believing that about 2 per cent probably had local origin in Kansas, 

 Oklahoma and Texas. 



DISTRIBUTING AGENCIES. 



The importance of distributing agencies is exaggerated in Okla- 

 homa by the fact that 95 per cent of our species do not extend entirely 

 over the State. The present distribution of many species is comparatively 

 recent, for the details of their ranges are determined by local soil and 

 vater conditions that have been developed within a comparatively brief 

 past. The western limits of many of our eastern species have numerous 

 slender extensions or outlying stations in the regions west of them, these 

 being mostly strips following the valleys and canyons of streams up their 

 courses. 



Two of the most generally distributed species in the Sitate are 

 Carolina poplar {populus deltoides), am/d long-leafed willow {Salix 

 longifolia). Their wide range depends upon the facts that appropriate 

 soil and moisture conditions for them exist over most of the State, and 

 that the species have been able to reach the stations where now found. 

 The wind is doubtless the agency responsible for the wide distribution 

 of these, as well as for numerous others iblown as tumlble-weeds or whose 

 seeds have pappus or coma of such nature as to enable them to be carried 

 by the wind, notable examples being found among our composites and 

 milkweeds. 



As far as our eastern species are concerned, the consideration of 

 water as a distributing agency may be discarded. Our rivers all flow 



