1905] WHITFORD—FORESTS OF FLATHEAD VALLEY 117 
regions, except along water courses, and are present in the Marquette 
region where they are more successful than conifers. 
The winter distribution of rain is of extreme importance, especially 
to those trees that hold their leaves, for KusANo'! has shown that 
evergreen leaves transpire considerably even at temperatures below 
freezing. While there are no data to show whether the bare twigs 
of deciduous trees transpire more or less than those of conifers, yet 
a prior it is very likely that they give off less moisture, for they have 
less surface. If this be the case, conifers are more in danger of 
desiccation during the winter months than deciduous trees; for even 
though the amount of evaporated moisture is slight, it must be remem- 
bered that the ground may be cold or even frozen, and that absorp- 
tion is thus checked. However, if the rainfall is sufficient and the 
relative humidity of the atmosphere is high, this danger is less. The 
figures will show that the winter rainfall of the Puget Sound region 
is excessive, while that of the Flathead valley and the northern 
peninsula of Michigan is equal in quantity to the summer rainfall. 
Conifers exist in all three situations. The extensive rainfall in the 
Winter months at Seattle must be coupled with the fact that the 
temperature conditions during these and the early spring months are 
exceedingly favorable to certain physiological processes and account 
for the almost tropical luxuriance of the trees of that region. 
RELATIVE HUMIDITY. 
The relative humidity of the atmosphere is another factor closely 
associated with the amount of rainfall. The drier the atmosphere 
the greater the transpiration. Other things being equal, the nearer 
relative humidity is to absolute humidity, the less water will the trees 
give off, and the less danger will there be of their desiccation. The 
greater the saturation deficit, the greater the danger of losing water. 
The following table will show the mean monthly deficits of the three 
stations to be considered. Unfortunately there are no data from 
Columbia Falls. 
The high averages of the saturation deficit for July and August for 
Kalispell, together with the small rainfall, probably account for the 
™t Kusano, S., Transpiration of evergreen trees in winter. Jour. Coll. Sci. Tokyo 
00: 313-366. 1902. 
