304 MINNESOTA BOTANICAL STUDIES. 
nesota slough, is about twelve miles in length. There are 
three small branches, one of which has, within the last decade, 
become considerably smaller than it formerly was, on account 
of the drying up of several springs near its source. The 
amount of water discharged from each of the two main creeks 
during the summer months is probably not less than 1,500,000 
cubic feet per day. Neither creek is very susceptible to 
changes of season, but either one will rise very rapidly after a 
sudden heavy rain-fall and return to its usual level in a few 
hours. 
The bluffs are high and steep, and not adapted to cultivation. 
(Plates XXII. and XXVI.) However, many of the ridges are 
cultivated and form some of the best farms in this part of the state. 
The valleys being subject to overflow and the bluffs very steep, 
by no means the entire area is adapted to cultivation. This 
condition is very favorable for the collection of native plants. 
The valleys are narrow, in no place exceeding a mile in 
width from the brow of one bluff to the brow of the one op- 
posite. 
In taking a view of the ecological groups of the plants in- 
habiting this region, the territory may, for convenience, be 
divided into river valley, creek valleys and bluffs. 
The river valley is so distinct from the creek vaileys that it is 
almost imperative that it be considered separately. The bluffs 
along the river vary somewhat from the other bluffs, but not 
sufficiently to warrant a division into river bluff and creek 
bluff. 
fiver valley.—tin the river valley I include the area from the 
foot of the bluffs on one side of the river, to the foot of the 
bluffs on the opposite side, not including any tributaries. Along 
this stretch of the river, from New Albin, Iowa, to Brownsville, 
Minnesota, the valley varies from three to five miles in width. 
The main channel of the river is from one-half a mile to a mile 
wide. The remainder of the area between the bluffs is formed 
of islands, sloughs and lakes during most of the year. (Plate 
XXV.,B.) During the spring and early summer the whole area 
is generally flooded so that collection can be carried on only dur- 
ing the late summer and autumn. The river channel proper is 
not a fruitful field for the collection of higher plants. The 
sluggish sloughs, lakes and ponds, however, offer excellent 
conditions for such collection. 
