434 APPENDIX. 



These data are the result of observations at sixteen stations 

 for about 150 years. 



The table show.s that in the warm season 30 per cent of the 

 rainfall in the open fields fails to reach the gauges under the 

 trees. Taking all seasons together, 25 per cent is intercepted. 

 This deficit does not include the water which drips from the 

 leaves, for this is fairly accounted for by the gauges. It is the 

 water which moistens the tree and its various parts and that 

 which flows down the trunk. The former is evaporated with- 

 out reaching the soil ; the latter reaches the soil finally, and 

 is measurable. Some experiments have indicated this amount 

 to be about 8 per cent of the precipitation. 



The same difficulties experienced with rain gauges are also 

 found to attach to thermometers ; the best thermometers 

 placed side by side will vary by as much as i .6° F. and 

 usually 0.7° F., hence small differences of temperature may be 

 merely inaccuracies, or due to non-uniformity of conditions, 

 and cannot be argued as a result of forest influences. 



P. 6g. Details of Meteorological Conditions within and out- 

 side of Forests. — The following conclusions have been drawn 

 from the German observations and are reproduced from the 

 above-cited bulletin : — 



Difference of Meteorological Conditions Within 

 AND Without the Forest. 



(i) Soil Temperatures. — The general influence of the 

 forest on soil temperatures is a cooling one, due to the shade 

 and to the longer retention of moisture in the forest floor as 

 well as in the forest air, which must be evaporated before the 

 ground can be warmed. As a consequence, the extremes of 

 high and low temperature within the forest soil occur much 

 later than in the open, and both extremes are reduced, but the 

 extreme summer temperatures much more than the winter 

 temperatures. 



The difference between evergreen and deciduous forests, 

 which almost vanishes in the winter time, is in fevor of the 



