Climate of Middle Illinois. 



29 



Table 12. 



OBSERVATIONS OF PRECIPITATION REDUCED TO ONE 



THOUSAND FOR EACH WIND. 



December , 

 January . . . 

 February . 

 March . . . , 



April 



May 



June 



July 



August . . . 

 September 

 October ... 

 November. 



Winter . . . . 



Spring 



Summer . . . 

 Fall 



Year 



East. 



180 



167 



146 



128 



148 



115 



95 



81 



57 



94 



79 



111 



164 

 130 



77 

 94 



111 



Xorth 

 West. 



123 

 130 

 130 

 115 

 109 

 136 

 194 

 121 

 143 

 120 

 113 

 112 



126 

 117 

 147 

 114 



124 



VEGETATION. 



The floral district of the upper Mississippi, as I understand it, will 

 comprise the southern part of Wisconsin from about the '44° N. L. Min- 

 nesota, from 46° N. L. southward, the greater southeastern part of Iowa 

 the wooded eastern borders of Nebraska and Kansas. Missouri, northwest- 

 ern Arkansas with the eastern borders of Indian Territory, and, finally, 

 Illinois — except the southern and southeastern borders along the Ohio 

 and lower Wabash (Ohio flora). There may be added the prairie land of 

 northwest Indiana, but the shores of Michigan Lake all around, should be 

 excluded as a part of the Canada flora. The western line of this district 

 would nearly coincide with the limits of the palaeozoic formation on the 

 east, and the new red sandstone on the west side; but, as already said, it 

 is difficult to circumscribe a floral district by lines. Many western species 

 cross the Missouri into Iowa, and not a few the Mississippi into the Illinois 

 country and are found in the numerous and often extensive prairies between 

 the woodland. Therefore, the vegetation of the upper Mississippi should 

 be regarded a gradual transition between the woodland-flora of the Ohio 

 district and the prairie-flora of the western plains. 



There are good reasons to exclude that part of the State of Illinois 

 that is south of the dividing ridge crossing from the Wabash to the Miss- 

 issippi, with an elevation of about 150 meter above the country both sides. 

 There are no prairies in this district of tertiary formation, and the com- 

 mon forest trees are such that do not occur north of the dividing ridge, 

 or only rarely, and not far northward, but all are common on the Ohio 



