514 CORRELATION OF DISTRIBUTIONAL FEATURES. 



The amplitude of evaporation conditions is much narrower in the 

 eastern section than in the western, agreeing closely, as already stated, 

 with the amplitude and values for the Southeastern Mesophytic Ever- 

 green Forest. The humidity conditions also exhibit a much narrower 

 amplitude, although they nowhere reach in the East the maximum 

 values that are to be found at the Pacific coast stations of the western 

 section. The moisture ratios all exhibit higher values for the eastern 

 section, and the ratio tt/E for the frostless season fails to overlap with 

 the range of this condition in the western section (see fig. 25). Here 

 again there is a close correspondence between the Evergreen Meso- 

 phytic Forests of the Northeastern and the Southeastern States. The 

 sunshine values are low and of narrow amplitude for the Northeastern 

 Evergreen Forest, the maximum value for this region being lower than 

 the maximum in any of the other vegetational areas. 



The moisture-temperature index for the eastern section ranges from 

 a minimum value which is slightly above the maximum for the western 

 section to a maximum which nearly coincides with that for the North- 

 western Hygrophytic Evergreen Forest. The close correspondence 

 between the range of this condition in the last-named region and in 

 the eastern section of the mesophytic forest doubtless affords a means 

 of explaining the features of resemblance between these two vegeta- 

 tions, which are so widely separated in the United States but have a 

 narrow strip of connecting forest in Canada. 



The Climatic Conditions for Evergreen and Deciduous Forests. — In 

 connection with the inquiry into the climatic conditions characterizing 

 the vegetational areas, a comparison has been made of the climatic 

 extremes for the Deciduous Forest and for the four evergreen forest 

 areas considered collectively. In figure 36 are shown graphs for the 



TtMPeii»TuRe 

 D..S .X Normal Fhostles. Season (F. SJ .. . r-..; v;vv- - ,. . v. . ■ . .. ......»»».,.,v>,.v» ,».. 



Hot Days. F. S. ^ ..,.,.,.,, ^t^,;, ■■ v ■;.■ v -■»■ ;,»^^ 



Cold Days, F. S. ggjggjg^gggggjjgj^ggjgggjg^gjgjggg^ 



Pmysiolocicai. Summation. F. S. bi^HHBBi^HaBiaaaMiMiMiiiliattAgiMiii^iJH 



Normal Daily Mcan. coldest 14 days of Year [ i—iwiw^M^witMiiiiMMisiMi^wiii^^M^^ 



Normal Daily Mean. Year taHM^BMai^i^MaMMM^M^tei^^^M^UitfUl^Wia 



Precipitation 



Normal Daily Mean. F. S. | ,„^^^^^^^^^^^^^^^^^j^^^^^^^^,^g; 



Days in longest Normal Rainy Period. F. S. ^j^^gjBgjjggjg^^gggBjjjjgjSjSiBSaaiBBIBaSm 



Days in longest Normal Dry Period, F. S. m^^ggMMM^Mb^^H^^b 



Mean Total. Year I ^^^^^^^^^^^^j^^^^^jjg^ 



Evaporation 



Daily Mean. 1687-8, F. S. g^^^g^ggBSlBiBiBSilBli 



Moisture Ratios 

 Normal P/E, F. S. bn^HBaMMiiiiiiiMiiiiiiiiAM 



Normal n/E. F. S. ^g^jg^^gggggggg^g^^ 



Normal P/C, Year ^^jgjgjjg^^^j^ggjggjgjgj^ 



Humidity 



Normal Mean. F, S. I ^^^^^^mmm^^^MBi 



Sunshine 



' r • f f / / *rr fn 



Normal Daily Duration. F. S ^^^^ggg^ggg^^^^gg^^^ggg^^^^^^ 



Moisture-Temperature Indices 



Normal P/e X T. F S.. Physiological Method """""""" 'iW 'ii'i" '{{{' U '{{TXHl 



/ f f r } fTTT 



Fig. 36. Contrasted climatic extremes for Evergreen (black) and Deciduous (shaded) Forests. 



