504 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



the amplitude of its normal daily mean is less, and also that of its num- 

 ber of days in the longest normal dry period. The lowest values for 

 the daily mean evaporation are very similar in the Grassland and the 

 Transition, but the much narrower amplitude in the Transition region 

 gives it much lower maximum values (0.166 inch as compared with 

 0.275 inch). 



The moisture ratios show a narrower ampUtude in the Transition 

 region than they do in either the Grassland or the Deciduous Forest, 

 falling, in general, between the values for these regions, as has been 

 shown in the earlier discussion. The narrow amplitude of the moisture 

 ratios and of relative humidity would point to these conditions as 

 having a strong controlling importance for the Transition region. Its 

 western edge coincides with the eastern edge of the Grassland and the 

 conditions with regard to the moisture ratio along that line have just 

 been mentioned. Along the eastern edge of the Transition region there 

 is not a close correspondence with any of the isoclimatic lines of the 

 moisture ratio, although there is a good agreement with the line for 

 0.110 in the north and an approximation to the interpolated line for 

 0.90 in the south. The Transition region lies almost precisely over the 

 area that is comprised between the lines for 65 per cent and 70 per cent 

 normal mean relative humidity for the frostless season, pointing to a 

 strong controlling importance in this condition. 



Deciduous Forest (fig. 31). — The leading temperature conditions of 

 the Deciduous Forest are of an intermediate character as compared 

 with those of the entire country, reaching an extreme value only in the 

 case of the minimum number of cold days. The amplitude of these 

 conditions is, in general, similar to that found in the Grassland and 

 the Grassland Deciduous-Forest Transition, although the north-south 



TCMPCRATUftC 



Dav» in Nohmal Fhostlcs* Sca«on <T. S.) I 



Hot DaVs. F, S. 



Cold Days, F. S. 



Pmvsiological Summation. F. S. 



Normal Daily Mean, coldcst 14 oays op Year 



Normal Daily Mcan. Ycar 



Precipitation 

 Normal Daily Mean. F. S. 

 Days in longest Normal Rainy Period, F. S. 

 Days in longest Normal Dry Period. F. S. 

 Mean Total. Year 



Cvaroration 

 Daily Mean. 1867-8, F. S. 



Moisture Ratios 

 Normal P/E. F. S. 

 Normal n/Z. F. S. 

 Normal P/E, Year 



Humidity 

 Normal Mean, F. S. 



Sunshine 

 Normal Daily Duration. F. S. 



Moisturc-Tempcrature Indices 

 NoRMAt P/C X T, F. S.. Physiological Method 



Fig. 31. Climatic extremes for Deciduous Forest. 



