TRANSACTIONS OF SECTION K. 863 



Across the central part of the State a broad belt of sand-hills stretches from 

 north-east to south-west. From these arise many small rivers of clear water, 

 filtered through the sands, and issuing in never-failing springs. Thus arise the 

 Middle Loup, North Loup, Calamus, South Loup, Shell, and the Elkhorn Rivers 

 and their numerous branches. Lastly, in the basin of the south-eastern quarter 

 there flow in different directions several alluvial streams, whose muddy waters run 

 sluggishly into the Republican, the Missouri, and the Platte Rivers. 



South-eastward of this area lie the heavy forests which characterise many 

 portions of Missouri. Southward lies the southern extension of the Great Plains, 

 while northward the plains continue to the international boundary and far beyond. 

 Eastward lie the undulating prairies of Iowa, with their streams bordered by 

 narrow belts of forest trees. Westward are the forests of the Rocky Mountains, 

 extending eastward upon the Black Hills of South Dakota, and the foot-hills of 

 Wyoming and Western Nebraska, namely Pine Ridge, north of the Niobrara River 

 and Cheyenne Ridge, between the North Platte and Lodge Pole Rivers. 



In this area, in the centre of the plains, the native trees of the South-eastern 

 Missouri forests, and the Western Rocky Mountain forests have pushed until there 

 are now about sixty-five species of trees which grow naturally within its limits. 

 Of this number fully fifty-six came from the Missouri forests, and but nine from 

 the Rocky Mountains. 



4. The Vegetation Regions of the Prairie Province. 

 By RoscoE Pound and Frederic E. Clements. 



A portion of the paper is devoted to a critique of the treatment accorded by 

 various authors to the floral covering of the North American continent, and in 

 particular to that given by Drude in his ' Handbuch der Pflanzengeographie.' 

 Especial attention is paid to the latter's characterisation of the Great Plains, and 

 the details are discussed at considerable length. The authors endeavour to demon- 

 strate the integrity of the Great Plains as a single vegetation province, and, in so 

 doing, summarise the most salient features of the floristic. Finally, the vegetation 

 regions of the prairie province are outUned briefly, followed by a concise summary 

 of the characteristic formations. 



There are three general classes of formations, comprising a considerable number 

 of types, viz., the prairie formations, prairie-grass, buff"alo-grass formations, the 

 sand-hill formations, bunch-grass, blowout, and sand-draw formations, the foot- 

 hill formations, the undershrub formation of tableland and bad land, the mat and 

 rosette formation of buttes and hills, and the grass formation of high prairie and 

 sandy plains.. 



5. The Zonal Constitution and Disposition of Plant Formations. 

 By Frederic E. Clements. 



The author has here reviewed the phy togeographical contributions bearing upon 

 the subject in hand, with especial reference to the part they have played in the 

 elaboration of the conception of zonation. In addition, he has endeavoured to 

 demonstrate the fundamental universality of zonation in all divisions of the floral 

 covering. The essential connection between lines of stress which are physical, 

 tensions which are biological, and zones which are phytogeographical is brouo-hfc 

 out, and the causation of these phenomena briefly discussed. Lines of stress are 

 symmetrical or asymmetrical. Continental lines of stress are asymmetrical. They 

 are transverse, in which case they are primary, and give rise to vegetation zones 

 or longitudinal, when they are secondary, and originate vegetation provinces. 

 There are also tertiary lines of stress, which are likewise asymmetrical, and define 

 vegetation regions. Symmetrical lines of stress produce bilaterally or radially 

 symmetrical tensions. Each may be the result of biological or topoo'raphical 

 symmetry, so that various portions of the floral covering may manifest zonation 



