324 



BOTANICAL SURVEY OF DISMAL SWAMP REGION, 



folk; Messrs. H. IT. Kirn and J. T. Griffin, of West Norfolk; Mr. T. J. 

 Harlow, of Portsmouth; Mr. Cannon, of the Albemarle >ind Chesa- 

 peake Canal Company; Mr. "Wallace, of Wallaceton, Va., find Messrs. 

 Willet, E. S. Meadows, and Cromwell, of Newbern, N. C. 



CLIMATE. 



The following data concerning the climate of the Dismal Swamp 

 region have been communicated by the United States Weather 

 Bureau. 1 Statistics are given from two stations in the region — 

 Norfolk and Cape Henry, Va. The climate at Norfolk closely tal- 

 lies with that of the Dismal Swamp itself, while at Cape Henry we 

 find the more extreme meteorological conditions to which the strand 

 vegetation of the region is exposed. In addition, data from the sta- 

 tions at Hatteras and at Wilmington, N. C, are presented. These 

 points are considerably south of the Dismal Swamp region, but they 

 are near enough to make a comparison of their climates with that of 

 the more northern stations interesting and instructive. 



TEMPERATURE. 

 THERMOMETRICAL RECORD. 



The normal number of days per annum with a temperature above 

 6° C. (4)3° F.) is, at Norfolk, 295; at Hatteras, 365. During this period 

 the normal sum total of daily temperatures above 6° C. (43° F.) is, at 

 Norfolk, 3,350.4° C. (6,047° F.); at Hatteras, 3,749.4° C. (6,749° F.). 2 



The normal mean temperature of the six consecutive hottest weeks 

 of the year is, at Norfolk, 26.3° C. (79.3° F.); at Hatteras, 25.9° C. 

 (78.6° F.). 8 



Normal temperature. 4 



Station. 



Jan. 



Feb. Mar. Apr. 

 6.0 ; 8.3 13.4 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



An- 

 nual. 



Norfolk j°£ ' 



4.6 



l'.i, 1 



.23. 9 



25. 8 24. 8 



21.7 



15.9 



10.2 



6.0 



15.0 



40.4 



42.8 1 46.0 66.8 



66.4 75.1 



78. 5 76. 6 



71.1 60.6 



50.3 



42.8 



59. 



for" 



Capo Henry . . < p 



4.5 



6.6 7.3 13.6 



18.0 1 22.8 



25.0 



24.7 



22. 1 1 16. 5 



11. 



6.6 



14.8 



40. 2 



43.9 ' 45.2 . 54.6 



64.5 ! 73.1 



77.0 



76.4 



71.8 61.8 



51.9 



43.9 



58.7 



Hatteras "if p " 



7.6 



8.1 10. 14.0 



19.1 23.3 



25.5 



25.2 



23.2 18.0 



13.1 



9.0 



16.3 



45.7 



46.6 50.1 57.2 



66. 4 74. 



77.9 



77.4 



73.7 04.5 



556 48.2 



61.4 



Wilmington J p ' 



8.3 



9.9 12.2 16.4 



20. 9 24, 8 



28. 5 



25.7 



23.1 17.5 



12.6 



9.0 



17.2 



46.9 



49.8 53.9 i 61.5 



69.7 76.7 



79.7 



78.2 



73.6 



63.5 



54.6 



48.3 



63.0 



1 For an account of the methods of computation and reduction employed by the Weather 

 Bureau see Report of the Chief for 1891-92, p. 37; also for 1890-97, pp. 126. 127, and 279. 



Q The sum total of effective temperatures, as here defined, is the factor upon which Dr. Mer- 

 riam bases the boreal limit of the transcontinental life zones in North America. Sec Nat. Geo- 

 graphic Mag., vol. 6, pp. 229 to 238 (1894), and Yearbook U. S. Dept. Agr. for 1894, pp. 211 to 213 

 (1895). 



3 The moan temperature of the six consecutive hottest weeks is tlie factor regarded by Dr. 

 Merriam (loc. cit.l as most effective in determining the austral limit of species. 



< All readings in these tables were taken in the shade. 



