(337) 



trifle lower than New York in spite of its drier appearance, is 

 probably accounted for by the slightly lower air temperature. 

 The evaporation at the Ithaca hemlock station was only .2 c.c. 

 lower than the New Haven ridge top, possibly accounted for by 

 being a little cooler, and only .4 c.c lower than New York. 



The similarity between the evaporation in widely separated 

 hemlock forests is rendered all the more striking by the small 

 difference between such extreme examples of the type as the two 

 stations on Saltonstall Ridge near New Haven. The ridge top 

 was about as dry looking a hemlock site as one could find, while 

 the north slope was moist and obviously favorable. In fact, as 

 noted above, the stations were selected to bring out the contrasts 

 between dry and moist hemlock forests. Yet the difference 

 between the rate of evaporation under the two sites was only 1.7 

 c.c. per day for the season. Expressed in terms of percentages, 

 the evaporation on the favorable site was only 14 per cent lower 

 than that on the dry site. In terms of New York hemlock as 

 100, the New Haven ridge top was 98, and the north slope 84. 

 Thus, excluding Cranberry Lake for the moment, the total 

 range between extreme hemlock sites about 300 miles apart was 

 only 1.9 c.c. per day, or 16 per cent. Yet the difference between 

 the hemlock and hardwood forests on the New York Botanical 

 Garden grounds about the same number of yards apart was 3.3 

 c.c. per day, or 29 per cent. 



Even when Cranberry Lake is included, the difference in rate 

 of evaporation between the extreme north and south examples of 

 hemlock is only 4.7 c.c. per day. In terms of New York as 100, 

 Cranberry Lake is 62. 



The natural tendency would be to discount a considerable part 

 of these results on the ground of their covering only a single 

 season, if it were not for similar work on Mt. Desert Island, 

 Maine, covering three seasons representing extremely dry and 

 unusually wet summers. The Mt. Desert results showed that 

 the relations between the forest types remained nearly the 

 same throughout the different seasons. The actual amount of 

 evaporation was different, though not very much so in the two 

 dry years, but the percentage relations of the forest types held 

 consistently. For example, the evaporation at the spruce 

 station during the three years, expressed in terms of the pitch 

 pine forest as 100, was 28, 24 and 29. The middle number 



