CORRELATION OF DISTRIBUTIONAL FEATURES. 501 



still more unlike in the general character of their climates, particularly 

 with respect to the seasonal distribution of precipitation and other 

 moisture conditions. In a more detailed study of climatic correlations 

 these two areas would repay separate investigation. 



The evidence of the amplitudes and also of the position of the iso- 

 climatic lines indicates that temperature conditions are of more impor- 

 tance in limiting the Semidesert than is the case with the Desert. 

 The normal daily mean of the coldest 14 days of the year appears 

 particularly to be of importance, ranging only from values slightly 

 below 45° to 54° for different sections of the region. The amplitudes 

 of the moisture ratios are greater than in the case of the Desert, and 

 the position of the isoclimatic lines corroborates this indication that 

 the conditions expressed by the ratios are not so important in the 

 limitation of the Semidesert. In passing from the coastal to the 

 interior portion of the Texas section of the Semidesert there is a 

 rapid fall in the values of the moisture ratio (plate 59) from 0.81 

 (Brownsville) to 0.35 (Fort Ringgold). A similar diversity in the 

 California section of the area is indicated by the value 0,10 for Fresno, 

 as compared with the value 0.45 for Los Angeles. The value for 

 Fresno is well above the minimum value for the Desert and the maxi- 

 mum values in each section of the area are well above the maximum 

 (0.27) for the Desert. 



Grassland (fig. 29). — The longest axis of the Grassland region runs 

 in a north-and-south direction nearly across the United States, with 

 the result that all of the leading temperature conditions exhibit wide 

 amplitudes within its boundaries. The number of cold days in the 

 frostless season runs through the entire gamut for the United States, 



TCMPCRATUAC 



Oitvs IN Normal rnosTLCSi ScAtON (F. S.) 

 Hot DAva, F. S. 



Cold Days, F. S. I 



Physiological Summation. F. S. f ' 



Normal Daily Mcan, coldcst 14 OAva or YcAfi dZ 



Normal Daily Mcan, Vcar I 



PflCCtPITATION 



Normal Daily Mean. F. S. t I 



Days in longest Normal Rainy Period, F. S 

 Days in longest Normal Dry Period, F. S. [ 

 Mean Total. Year 



Evaporation 

 Daily Mean. 1867-8, F. S. 



Moisture Ratios 

 Normal P/C. F. S. 

 Normal tt/e,. F. S. 

 Normal P/E, Year 



Humidity 

 Normal Mcan. F. S. I 



Sunshine 

 Normal Daily Duration. F. S. I 



MoiSTUHE-TCMPERATURe JnOICES 



Normal P/C i T. F. S., Phvsiolocicai. Method 1 M 



Fig. 28. Climatic extremes for Semidesert. 



