CORRELATION OF DISTRIBUTIONAL FEATUHES. 491 



similar vegetations. The longest frostless season is found in the South- 

 eastern Mesophytic Evergreen Forest, and the amplitude for that 

 vegetation is approximated by the Semidesert. Aside from the cases 

 mentioned, there is considerable dissimilarity between the amplitudes 

 of this condition in the various vegetations, particularly between the 

 Evergreen Forest areas. The amplitudes of the other areas overlap 

 to such an extent that in all five of them it is possible to find localities 

 with frostless seasons ranging from 197 to 245 days in length, that is, 

 from the minimum for Semidesert to the maximum for Grassland. 

 This same range of seasonal length may also be found in all of the 

 Evergreen Forest areas except the eastern section of the Northern 

 Mesophytic Evergreen Forest. 



Hot days (plate 35, fig. 21) . — The number of days with a normal daily 

 mean temperature of 68° or above is relatively uniform for the first 

 group of vegetations (group A), although reaching slightly lower 

 maximum values for Grassland and Grassland Deciduous-Forest 

 Transition. The Northwestern Hygrophytic Evergreen Forest has 

 no hot days in any part of its range, and portions of four other vegeta- 

 tional areas are also without hot days in this sense. The greatest num- 

 ber of hot days is encountered in the Southeastern Mesophytic Evergreen 

 Forest, where the range from 120 to 180 days, which is characteristic 

 of a large area in this vegetation, is raised to 365 days for Key West. 



Cold days (plate 36, fig. 22) . — The number of days with a normal daily 

 mean temperature of 32° or below is a climatic feature of great ampli- 

 tude for several of the second group of vegetations (group B). The 



TEMiicn*TuRC. D*vs IN Normal FnotTLiss 8tA*oi» 'F. 8J 



VCGETATIOH 25 365 



Desert 

 semi-desert 



GR»SS(-AN0 



gnassond-oeciduous-forcsttransition 

 Deciduous forest 



NORTHWESTERN HyGROPHTTK EVERGREEN FOREST 



Southeastern mesophytic Evergreen Forest 

 Northern Mesophytic Evergreen Forest iwest) 

 northern Mesophytic Evergreen forest iEasti 



vegetation f) 



desert a 



TeMrcRATuRE. Hot Days, F. S. 



^ ~1 



Grassland I ^ I 



ghassuno-oeaouous-foresttransmon 

 Deciduous Forest 



NORTHWESTERN HYGRonrmc Evergreen Foucct 

 Southeastern MESO«rmc Evebgrcen Forest 



NORTHERN MESOWYTIC EVERGREEN FOREST r WEST I 

 NORTHERN MES0(>HYTIC EVERGREEN FOREST 'EAm 



Fig. 21. 



