364 MINNESOTA BOTANICAL STUDIES. 



MESOPHYTIC FIELD VEGETATION. 



The mesophytic field vegetation as it exists in the creek valleys 

 to-day is almost entirely a result of cultivation. The table lands 

 which bear the plants of the mesophytic field were formerly al- 

 most entirely wooded. To-day they are cleared of timber and 

 used for cultivation. They furnish the best fields for cultivation 

 in the whole district. They are not subject to the overflow of 

 the bottom lands, nor to the drought of the ridges, nor to the 

 washouts of the side-hills. Being so extensively cultivated the 

 plants growing upon them, which are not themselves cultivated, 

 are almost confined to the edges of fields and thickets. Under 

 such conditions a list of plants of this area would have no bear- 

 ing upon the natural ecological groups. 



Bluffs. The bluffs bordering the river differ from those 

 bordering creek valleys in being steeper and in having many 

 more precipitous cliffs. The brow of the bluff along the river 

 for almost the entire distance bordering the territory covered ex- 

 cept where interrupted by branch valleys or ravines is one al- 

 most perpendicular limestone cliff, varying from a few feet to a 

 hundred feet in height. Cliffs of this sort are not so common 

 back from the river. The vegetation of the river bluffs differs 

 to some extent from the creek bluffs in its character. Some 

 of the common forest trees of the lowland of the creek valleys, 

 instead of growing on the lowland of the river valley inhabit 

 the foot of the river bluff. The proximity of the river 

 bluff to larger areas of water seems to raise the moisture 

 content of the soil of the river bluff above that of the creek 

 bluff at the same height above water level. The growth 

 then of such a tree as the black walnut at the foot of the river 

 bluff does not show that it grows here under more arid conditions 

 than in the creek valley, but that the same conditions of moisture 

 in the soil are found at a higher level on the river bluff than on 

 the creek bluff. 



On all bluffs the vegetation shows the greatest variation with 

 the direction of the slope. Those facing from south to west 

 and receiving the direct rays of the sun from noon to 4 P. M. 

 are generally bare of trees (Plate XXII., B) and shrubs while 

 those facing from north to east are generally thickly wooded 

 (Plate XXVI., B). Ravines with their greater amount of 

 moisture in the soil and greater protection from winds are 



