492 CORRELATION OF DISTRIBUTIONAL FEATURES. 



Grassland area exhibits the total range for the United States, from no 

 cold days in the south to 158 at the Canadian boundary, and the 

 Grassland Deciduous-Forest Transition shows nearly as great an 

 amplitude with respect to this condition. The two Semidesert areas 

 are without cold days, and the Desert area is surprisingly like the 

 Deciduous Forest in the amplitude and extremes of this condition. 

 The Northwestern Hygrophytic Evergreen Forest is also without 

 cold days, and the Southeastern Mesophytic Evergreen Forest ranges 

 from none to only 27 days at the coldest station. The two sections of 

 the Northern Mesophytic Evergreen Forest are very similar with 

 respect to this condition. 



Physiological temperature summation (plate 40, fig. 22). — The physio- 

 logical summation of temperature (expressed in thousands) exhibits 

 wide •amplitudes for the vegetations of group A (Desert to Deciduous 

 Forest) . The most striking feature brought out by a comparison of the 

 blocks is the relative similarity of the climatic dimensions for the vege- 

 tations of group A as compared with the unlikeness of the blocks for 

 those of group B (the Evergreen Forest regions) . The minimum value 

 for the United States and the smallest amplitude are exhibited by the 

 Northwestern Hygrophytic Evergreen Forest. The eastern and 

 western sections of the Northern Mesophytic Evergreen Forest are also 

 characterized by low summations, but they both reach much higher 

 maximum values than does the Northwestern Forest. The Southeast- 

 ern Mesophytic Evergreen Forest reaches the highest values of any 

 of the vegetations and also exhibits the greatest amplitude of this 

 condition. 



. TtMPCRATuRC. Colo D*vt. F. S. 



VESETATIOH J5g 



Desert 



semi-desert 



Grassland 



Grassland-Deciouous-FohestTransition 



Deciduous forest 



northwestern hrgrophttic evergreen forest i q 

 Southeastern Mesophytic Evergreen Forest 

 Northern Mesophytic Evergreen Forest (West) 

 Northern mesophytk Evergreen forest ieasti 



TCMPCNATURC. PHYSIOLOGICAL SUMMAtlON, F. S. 

 VEGETATION 1I.947 



Desert 



SemiDesert 



Grassland 



GRASSUND-OECIOUOUS-FORESlTlBUanwi 



Deciduous Forest 



Northwestern HtGROPnmc EVncHEEH FokesT 

 Southeastern mesophytic Evergreen Forest 

 Northern mesophytic Evergreen Forest (West) 

 Northern mesophytic Evercreen Foanr iHsr 



31J)63 



Fig. 22. 



