68 BROOKLYN BOTANIC GAREND MEMOIRS 



Taking into consideration that the days were considerably shorter 

 toward the end of the readings, it is certainly of significance that at each 

 period of high winds the black instrument shows marked increase in its 

 rate of evaporation. And if, as Bates and Burns have shown, it is a better 

 measure of actual transpiration than the white instrument, it may well be 

 that from the peak readings of the black instruments at Montauk we get 

 the best expression of the most unfavorable environmental conditions on 

 the Downs, and the best picture of, at least the probable effect of wind as 

 it keeps down the establishment on these Downs of almost everything but 

 grassland and bayberry thickets. No one who has visited Montauk when 

 one of these southwest summer winds is blowing, and the temperature is 

 high (for Montauk) can ever fail to be impressed with the unfavorable 

 effect it must be having on transpiration and growth. Coupled with soil 

 conditions, to be described presently, it is undoubtedly the chief factor in 

 keeping things as they are on the Downs. 



This high rate of evaporation and probably also of transpiration coin- 

 ciding with high winds does not conform to the results of Briggs and 

 Shantz.* They found that evaporation and transpiration were much 

 more sensitive to sunshine than to wind, and in fact discount the latter as a 

 factor of importance. That conclusion appears to fly in the face of most 

 practical gardeners' notions of the effect of wind on transplanted seedlings, 

 where, even if the ground be kept moist, wilting is more apt to occur in a 

 high wind than during a period of calm. An examination of the papers 

 cited shows that the highest wind velocity reached in their experiments is 

 13.5 miles per hour (given by them as 6 meters per second). It may well 

 be that such low velocities are much over-ridden by other factors such as 

 sunshine, as all their graphs show a remarkably close correlation between 

 transpiration, evaporation and sunshine, and almost no correlation between 

 these and changes of wind velocity. 



The wind, however, scarcely begins to blow at Montauk until it reaches 

 at least twenty-five miles an hour, and it certainly appears from the records 

 that at velocities of more than that it does have a decided effect. Nor can 

 the "high spots" in the black readings be attributed to specially clear days 

 with a maximum of sunshine. The accompanying tabulations of the con- 

 ditions and the graphs show that high evaporation from the black instru- 



* Jour. Agr. Res. 5: 583-649. 1916, on "Hourly Transpiration Rate on Clear Days 

 as Determined by Cyclic Environmental Factors;" loc. cit. 7: 155-212. 1916, on "Daily 

 Transpiration during the normal growth period and its correlation with the weather;" or 

 with loc. cit. 9: 277-292. 1917, on "Comparison of the hourly evaporation rate of atmo- 

 meters and free water surfaces with the transpiration rate of Medicago saliva." 



