330 



HOTAN1CAL SURVEY OK DLriMAL SWAMP REGION. 



WIND. 



The normal wind direction in midsummer is almost exactly opposite 

 to the normal direction in midwinter. In January the prevailing 

 winds at Norfolk are from slightly west of north; at Hatteras from 



almost, due north, and at Wilmington from considerably west of 

 north. In July, on the other hand, the prevailing winds at Norfolk 

 and at Wilmington arc from somewhat, west of south, and at Hatteras 

 from almost exactly southwest. 1 



Average maximum velocity of the wind. 



Station. 



fka 



\mi 



Cape Henry fe; 



Hatteras fe- 



|ks 



\mi. 



Norfolk 



Wilmington 



Jan. 



i;».t; 



9. 7 

 25. 5 

 15.8 

 25.0 

 15. 5 

 15.5 



9. 6 



l'Vb. 



1(5. li 

 10.3 

 35.2 

 15. « 

 24. 5 

 15.2 

 Iti.ti 



Mar. 



Apr. 



18.2 



15. a 



ll.il 



9.7 



30.3 



2!). 7 



18.8 



14.7 



25.2 



24.2 



15. li 



15.0 



18.2 



18.7 



11.3 



11. (i 



May, 



13.5 



8.4 

 21.(1 

 13.0 

 20. I 

 12.5 

 16.9 

 10.5 



JUIlO. 



July, 



Aug. 



Sopt. 



14.2 



12.!) 



13.2 



15. 2 



8.8 



8.0 



8.2 



9.4 



22.(1 



19.0 



20.8 



21.8 



13. (i 



11.8 



12. 9 



13. 5 



21.3 



18.5 



19.7 



17.3 



13.2 



11.5 



12.2 



10.7 



15. (i 



14.7 



13. 5 



14.2 



9.7 



9.1 



8.4 



8.8 



( tot, 



15. 9 



9.8 



22. I 

 13.9 

 18.4 

 111 

 L3.7 

 8.5 



Nov. 



li; .:; 

 Ki.l 

 23, 5 

 14. fl 

 19.8 

 12.3 

 [4.8 

 s.s 



Doc. 



An- 

 nual. 



15.0 

 9.3 

 21. s 

 15. 1 

 24.0 

 14.9 

 13.7 

 8.5 



15.2 

 9. 1 

 23, 2 

 11.1 

 21. 1 

 13.3 

 15.5 

 9, li 



The rate of movement of currents of air is of great importance to 

 vegetal ion, not only by reason of their direct mechanical effect upon 

 the plant and niton its substratum, but also because transpiration 

 increase's with the velocity of the wind, other things being equal. The 

 average maximum velocity of the wind varies greatly within the limits 

 of the Dismal Swamp region, the ratio of velocity at Cape Henry, one 

 of the most exposed points on the Atlantic coast of North America, to 

 that at Norfolk being nearly as 5 to -'5. The range in average maxi- 

 mum velocity from month to month does not greatly vary, as that in 

 the month of greatest (March) exceeds that in the month of least 

 (July) by about <}() per cent. 



SUMMARY. 



The climate 1 of the Dismal Swam]) region as a whole is highly favor- 

 aide in all essential respects to the vigorous growth of what, we may 

 term, for the sake of convenience, " normal " plants; i. e., such as are 

 not especially equipped to endure any kind of extreme conditions. It 

 is characterized by a long growing period with a relatively high sum 

 total of effective temperature, a mild winter, normally slight daily 

 variations of temperature, abundant sunshine, heavy and well dis- 

 tributed rainfall, and a high and remarkably uniform percentage of 

 atmospheric moisture. It is preeminently a forest climate, and the 

 whole region was, in its primitive condition, densely forested. There 

 still remain, especially in the depths of the Dismal Swamp, many 

 trees of great size. On the outer coast, however, among the sand 

 dunes, local qualities of the soil and extreme exposure to the wind 



1 See Rep. Chief U. S. Weather Bureau for 1896-97, charts 1 and 8. 



