116 BOTANICAL GAZETTE [FEBRUARY 
to enable forests to exist. It is very probable that farther to the east 
in the mountains there is a still greater quantity of rain. At least 
the character of the vegetation would suggest that this is the case, 
for here the forest growth approaches in luxuriance that of the Puget 
Sound region where the rainfall is much greater. 
A comparison of the rainfall in the valley with that of the Puget 
Sound region and of the northern peninsula of Michigan will lead 
to some interesting conclusions (Table IJ and fig. 10). In this com- 
parison the data at Columbia Falls will be used rather than those at 
Kalispell, for reasons that are at once apparent. The character of 
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IG. Renn: sates rainfall for Seattle ( —), Kalispell (———), Colum- 
bia Falls (——-—— -), and Marquette (-—---—--— ); the figures are millimeters of 
rainfall; summer rainfall highest at Marquette and exceedingly low at Seattle; in 
winter rainfall the reverse is true. 
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the distribution of the rainfall is of considerable importance. Thus 
at Marquette and Columbia Falls the rainfall is more or less evenly 
distributed thoughout the year, with the five warmest months, May, 
June, July, August, and September, having about half of the mois- 
ture. Thus these five months at Columbia Falls show a fall of 2747” 
out of a total of 543™™; and at Marquette 414™™ out of 823” 
On the other hand, Seattle with its total of 945™™ has only 202™™ 
during these months. It is a well-known fact that the broad-leaved 
deciduous trees evaporate more moisture during the summer months 
than do the narrow needle-like leaves of the conifers. It is very 
possible that the 202™™ at Seattle and even the 274™™ in the Flat 
head valley are not sufficient to maintain the broad-leaved deciduous 
trees in these climates. In any event, they are absent in the two 
