CHAPTER II. 

 PHYSIOGRAPHY AND GEOLOGY. 



INTRODUCTION. 



In any consideration of the plants of a region a word or two as to 

 the geography and geology of the latter cannot come amiss. Among the 

 various factors which influence the geographical distribution of plants, 

 such matters as altitude, diversity of surface relief, the character of the 

 soils and the conditions of water supply are all of first importance. These 

 are all more or less primarily dependent upon the geological structure of 

 the region. The factor of climate is more remotely related' to the same 

 thing. The methods of transportation, the density of population and 

 other industrial factors which are so largely modifying the early distribu- 

 tion of our common plants, also stand in definite relationship to the geol- 

 ogy and geography of the region. 



It is important to know the geographical and geological features of 

 the region from which any collection of plants has been made, particu- 

 larly when, as in the case of forage plants, it is desired to estimate the 

 advisability of introducing into other regions any of the plants, or of 

 bringing into the region foreign grasses or forage plants. It is a common 

 observation that certain grasses grow well in particular situations while 

 at neighboring points they sicken and die. While in some cases this is a 

 matter of climate as influenced by a north and south exposure, in a large 

 number of cases the preference which the plant exhibits is for a certain 

 soil. The flora of the driftless and drift-covered regions of Iowa, for 

 example, show the sharpest difference. It seemed best, accordingly, to give 

 a brief description of the physiography and geology of the region from 

 which the plants herein discussed were collected. 



PHYSIOGRAPHY. 



The Mississippi Valley forms one of the main physiographic fea- 

 tures of America. From the gradually decreasing undulations of the 

 Appalachians it stretches unbroken westward to the abrupt foot hills of 



