_Studies of Forest Influences._ Studies on the influence of forests upon stream flow and erosion are attempting to furnish important data for American conditions upon this subject. At the Wagon Wheel Gap Forest Experiment Station in Colorado such a study is being carried on. The purpose of the study for the first two or three years has been to determine the character of the two streams which are to be measured. The forest cover on the two watersheds is practically identical. The results so far obtained indicate that the influence upon the stream flow must be about the same in both cases, and, consequently, a comparison of these streams after the denudation of one watershed will be a very fair test of the influence of the forest cover upon the relative height of the flood stage and low-water stage, the amount of erosion, and the rate of melting of the snow. [Illustration: Figure 29. At the Fort Valley Forest Experiment Station, Coconino National Forest, Arizona. A typical meteorological station Forest officer measuring precipitation. Note the shelter which contains thermometers and also the electrically equipped instruments to record the direction and velocity of the wind.] [Illustration: Figure 30. Forest officer ascertaining the amount of evaporation from a free water surface. Fort Valley Forest Experiment Station, Flagstaff, Arizona.] Experimental observations which have been conducted since 1908 at the various Forest Experiment Stations have shown that the forest exercises a decided moderating influence upon temperature extremes, wind motion, and evaporation. Likewise, the presence of a forest cover retards the melting of snow in the spring, and in this way huge snowbanks in the forests feed the nearby streams until late in the summer. Forests therefore have been shown to conserve the water supply and also causing this water to run off slowly rather than in sudden floods. Studies have also been conducted on determining the effect of cutting timber upon the climate within the forest.