and fresh. It is for this reason that in areas occupied by a suc- 

 cession of ridges, as on the southeast shore of East Okoboji lake 

 and in the Hottes lake region, the forest extends even over the 

 tops of the ridges. 



The two rather large forest areas at Arnold 's Park and on the 

 peninsula between Miller and Emerson bays evidently owe their 

 existence to the fact that they are partly surrounded by water, 

 and that there are sufficient irregularities in the surface for a 

 forest beginning. The peninsula between the bays is also pene- 

 trated by swamps, and a large swamp cuts it off from the prairie 

 region to the west. Even with this advantage the western bor- 

 der of the forest is decidedly xerophytic, as is shown later. 



One of the interesting treeless areas is that which lies north of 

 Miller's Bay. It is shown in Plate II, fig. 1, and Plate VIII, 

 fig. 3. Here the prairie extends down almost to the border of 

 the lake. There are no abrupt slopes, and no groves. The 

 opinion has been expressed by local observers that perhaps the 

 Indians had burned the forest on this side. There is no evidence 

 to show that a forest had ever existed here. Indeed the 

 evidence at hand shows that this slope rising to the north has 

 been exposed to exactly the same conditions as the general 

 prairie, and that notwithstanding its proximity to the bay it is 

 decidedly xerophytic. 



On this slope stations were also installed at several points 

 along a line 660 yards east of the west line of section 23, Tp. 99 

 N., R. 37 W., and Mr. Boot made a series of observations similar to 

 those made in section 16, Tp. 99 N., R. 36 W. The observations for 

 one day, illustrating the general result, are here recorded.^ The 

 day selected was June 26th, 1913. The wind was from the south 

 and the temperature varied from 74° to 86° at station ''a" 

 (practically in the lake) and 75° to 90° F. at station ''d." The 

 observations were made at intervals from 8 :00 a. m. to 6 :00 p. m. 

 The velocity of the wind varied little from six miles per hour at 

 the several stations. The results are here given, the variation in 

 relative humidity at the several stations being given in the first 

 line, and evaporation as before measured in tenths of a cubic 

 inch in the second line, and in cubic centimeters in the third 

 line. 



7 Mr. Boot will publish a more detailed account of these observations. 



20 



