CORRELATION OF DISTRIBUTIONAL FEATURES. 539 



graphs exhibiting these extremes are such as would be secured by a 

 superposition of the graphs for the two vegetations. 



In spite of the great north-and-south extension of the range of 

 Pseudotsuga, it encounters a narrow amphtude of conditions in the 

 number of hot days in the frostless season and in the physiological 

 summation of temperature. Further climatological data from stations 

 situated within the range of this tree at some of its most southerly 

 localities might broaden the amplitude of these conditions, giving 

 values more nearly like those for the western section of the Northern 

 Evergreen Forest, which area is drawn in a more generalized manner. 



With respect to all of the conditions involving precipitation or 

 atmospheric moisture, the amplitudes are very wide, being in many 

 cases a superposition of the amplitudes for the two forest areas men- 

 tioned. The fact that this tree is so nearly coextensive with the 

 southernmost areas of Mesophytic Evergreen Forest may be taken to 

 mean that the constellations of conditions by which its range is limited 

 are very similar to those limiting this forest. The lowest normal daily 

 mean precipitation, the highest values for evaporation, and the lowest 

 ones for the moisture ratios are all to be regarded as important in 

 hmiting the southward range of this tree. Although the lower limit of 

 Pseudotsuga in the mountains of Arizona and New Mexico is slightly 

 higher than the lower limit of the pines which form the edge of the 

 Mesophytic Forest, the data from the few stations in that region show 

 a close correspondence in the extremes just mentioned. The number 

 of hot days and the value of the physiological summation of tempera- 



T(Hmi*Tu«c 



D*TS IN Normal Fhostlem SciMON (F. S.I M 



Mot D*v«. F. S. ■ 



CoiD Dav*. F. S. U 



Phvciolocical Summation. F. S. I 



NOKMAl OaiLT MCAN, COIOCST 14 DAT* Of VUN [I 



NoKMAi. Daily Mcah. Yum C 



Precipitation 



Normal Daily Mcan. F. S. C 



Dat* in lonsut Normal Rainy Period, F. S. ■ 



Days in lonocst Normal Dry Pcrioo, F. S. C 



Mean Total, Viar C 



Evaporation 



Daily Mcan. ISeT-S, F. S. | 



Moisture Ratios 

 Normal P/E, F. S. O 



Normal n/Z, F. S. d 



Normal P/E, Year CI 



Humioitt 

 Normal Mean, F- S. LZ 



Sunshine 

 MoRMAL OAII.Y Duration. F. S. CZ 



Moisture-Temperature Indices 

 MoMiAL P/E I T, F. S., Physiolocical Method 1 -| 



Fig. 47. Climatic extremes for Pseudotsuga mucronata. y^\'0^^'4/ ,- 



\^>\ ^ 

 \^> -- 



