> 



338 BOTANICAL GAZETTE [November 



mountains at Boulder bears in a crevice a young specimen of yellow 

 pine.^ Occasionally Celtis reticulata^ a representative of the eastern 

 forestSj is found invading this formation. 



r 



The absence of a secondary layer v^here the pines and Douglas 

 firs grow densely is not to be explained alone on the ground of a 

 scarcity of light or of moisture, but rather by the combined absence 

 ' of these factors. The shade is seldom dense enough to exclude 

 shade-loving plants, were sufficient moisture present to satisfy the 

 needs of such forms. 



I 



The physical factors of this formation were taken at an altitude 

 of about 2100"^ on a north slope in a small grove of pines and Douglas 

 firs. The results are given below: 



Temperatxires 



(Observations July 29, 12:15 P. M.j August 14, 5:15?. M.*, September 13, 3:40 P. M.) 



_22.5cnl —11,25*="^ 0«°^ +7.5*=°* +9^"» 



Minima i6?2 * 19^=^ i8?75 2i?75 22° 



Maxima 17.25* 20°* 26° 27^ 26?75 



* Two observations. 



Relative humidity 



(Observations July 29, 12:15 p. m,; August 14, 5:15 p. ii.; September 13. 3-4^ '^- ^•) 



7.5«m 



rim 



Minima 21 per cent 23 per cent. 



Maxima ...... 65 per cent. 35 per cent. 



Water content 



Observations it.25«" 22.5 — 11.25 



July 



August 



-cm 



4.4 per cent. 



2.6 per cent 



September 3. . . . 1.6 per cent. 2 , i per cent 



Light values 



r 



September 13 3:40 p. m. =4 : 60 (in medium shade) 



4 : 360 (in direct shade of tree trunk) 



(4) 



ih 



orum 



2400^ altitude and stands 



flexilis formation on the other, though it is overlapped by each of these, 

 and indeed the two latter overlap each other at about this altitude. 

 The question may be raised whether the Pimis Murrayana forests 

 deservx recognition as an independent formation, or should be classed 



connection 



region 



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