266 



ENVIRONMENTAL CONDITIONS. 



Table 13. — Number of days in the period of the average frostless season with normal precipita- 

 tion of more than 0.10 inch and with Jiormal precipitation of 0.10 inch or less, the latter 

 also expressed as percentage of the number of days in the average frostless season. (Plates 

 47, 48, and 49.)— Continued. 



The values representing the number of normally rainy days in the 

 period of the average frostless season were plotted in the regular way 

 and the resulting chart is given as plate 47. This chart shows isocli- 

 matic lines at intervals of 25 days; the total range for the country is 

 from 284 days (New Orleans, Louisiiana) to none at all (various sta- 

 tions in the arid region). The general zonation is seen to be very 

 similar to that shown in plate 46. The heavy lines show the four 

 provinces above described. 



(5) Number of Normally Dry Days in Period op Average Frostless Season. 



(Table 13, Plate 48.) 



This index is the complement of the preceding one, and is derived 

 by subtracting that from the number of days in the period, in each case. 

 A dry day is thus one that has a normal daily mean precipitation 

 (Bigelow, Bull. R) of 0.10 inch or less. If the former be considered as 



