218 The Plant World. 



may they be taken to represent what the writer might beheve 

 to be the truth, but merely what appears from the Hmited data 

 at hand. Everything considered, however, they probably do 

 not go far wrong, and seem at least worthy of consideration in 

 connection with the various non-quantitative theorizings and 

 rather academic discussions of present-dav ecologv. 



The evaporation chart (Fig. 3) prepared from the fifteen 

 weeks averages of the weekly water losses from the standard 

 porous cup atmometer, may be taken to represent for the sum- 

 mer season, 1908, the variations in the intensitv of evaporation 

 over the United States as accurately as the data at hand will 

 permit. The dotted portions of the isoatmic lines on the chart 

 have been tentatively inserted by an interpretation of the humid- 

 ity chart for the three summer months of the same year, data 

 therefor being taken from the Monthly Weather Review. For 

 some reason, impossible of defmtiton at present, the evaporation 

 data obtained from Bozeman and Salt Lake City are apparently 

 too low; no commensurately high humidity is indicated for these 

 stations. They have therefore been neglected in the preparation 

 of the chart. 



The most significant features of this chart are the following : 



(1) The Canadian region of low summer evaporation 

 extends southwestward from Lake Superior, as far as the valley 

 of the Arkansas River. It occupies the northern peninsula of 

 Michigan but not the southern. 



(2 Another southern extension of the northern area of 

 low evaporation intensity extends southwestward from southern 

 New England and occupies the whole of the Appalachian moun- 

 tain system south of Pennsvlvania. In the highest mountains, 

 of North Carolina, the average weekly rate is shown to be lower 

 than at Fredericton, N. B. 



(3) The valley of the lower Great Lakes is occupied by 

 an area of exceedingly high summer evaporation, which ap- 

 parently extends, roughly, over eastern Michigan, the penensula 

 of Ontario, and the state of New York. 



(4) The southeastern coast exhibits about the same evap- 

 oration rates as middle New England, \\estern ?klichigan, and 

 the Mississippi-Ohio valley. 



