526 CORRELATION OF DISTRIBUTIONAL FEATURES. 



correspondence of limiting values for the moisture conditions in the 

 Austroriparian and Carolinian. There is a very strong dissimilarity 

 between the moisture conditions for the Austroriparian and the Lower 

 Sonoran. The daily mean evaporation of the frostless season ranges 

 from 0.96 to 1.69 (?) in the former zone and from 104 to 273 in the 

 latter, thereby overlapping to a considerable extent. 



Several of the temperature conditions exhibit narrow amplitudes in 

 this zone, notably the number of cold days and the number of hot 

 days. A narrow amplitude is also exhibited -by the number of days 

 in the longest normal dry period of the frostless season, and in the 

 imperfectly determined data for the mean total precipitation for the 

 year and the normal mean humidity for the frostless season. It is 

 apparent from this evidence that the Austroriparian Zone is differ- 

 entiated from the adjacent zone on the north by temperature condi- 

 tions and from the adjacent one on the west by moisture conditions, 

 the greatest importance in this differentiation attaching to the con- 

 ditions of narrow amplitude which have been mentioned. 



2. DISCUSSION OF THE OBSERVATIONS. 



It is impossible to undertake a logical discussion of the correlation 

 of climatic conditions with the areas occupied by the life-zones, because 

 of the climatic basis on which these zones were originally outlined by 

 Merriam. The boundaries running, in general, in an east-and-west 

 direction were determined by the remainder temperature summation 

 above 32°, and the boundary running north and south along the one- 

 hundredth meridian was selected because it is a pronounced climatic 

 line, separating what would otherwise be very irreconcilable faunal and 

 floristic regions. From these considerations it may be seen that we 

 should be able to predict the nature of the conditions which limit 

 these areas. An examination of figures 37 to 42, indeed, shows that we 

 encounter marked differences in all of the temperature conditions on 

 passing southward from the Transition Zone, through the Upper 

 Sonoraif to the Lower Sonoran, or in passing from the Alleghanian 

 Zone down through the Carolinian and Austroriparian, barring a 

 rather strong similarity between these conditions for the Alleghanian 

 and Carolinian Zones. A comparison of Transition Zone with Alle- 

 ghanian, of LTpper Sonoran with Carolinian, and of Lower Sonoran 

 with Austroriparian, exhibits a similar marked difference of moisture 

 conditions. If the humid Transition of Washington and Oregon is 

 considered separately from the remainder of the Transition, this con- 

 trast becomes more striking in the first of these comparisons. 



As far as possible we have made use of Merriam' s maps of the 

 remainder summation. of temperatures above 32° F. and of the normal 

 daily mean temperature for the hottest 6 weeks of the year, but we 

 have been prevented from making as full use of these maps as their 



