PRECIPITATION UNDER TREES. 



107 



from April to June. The drop for deciduous trees during these months 

 is from a percentaiie of 77 to that of (K), then to 6~), making the foliage 

 catch hut 12 per (;ent of tlie iH^ecipitation, while the bare limbs and twigs 

 in March caught 14 per cent, and in April apparently 23 per cent. The 

 evergreen trees permit 73 per cent of the rainfall to pass through their 

 foliage in April and identically the same in June. Admitting (though 

 there arc some reasons for doubt) that the rainfall is actually the same 

 over a wood and a place outside but near, this small action of the foliage 

 as com])ared with the branches and twigs requires esidanation, and, 

 whatever the explanation nmy be, it must api)ly only to deciduous trees, 

 as evergreens show no difference in these months. No satisfactory 

 explanation occurs to me. The catch in winter is largely influenced 

 by the form of preci])itation, the snow being caught temporarily and 

 let fall later into the gauges below, but this would not affect the fall 

 from April on. 



..,^. DECIDUOUS TREES. EVERGREEN TREES. 



Fig. 55. — Percentage of precipitation, received under trees (dittereiit kinds). 



The foliage catches more of the rainfall during the warm season, even 

 in the case of deciduous trees. The percentages for the German stations 

 are as follows, the warm season being taken from May to September, 

 five months : 



(Jeiieral average 



Average for deciduous trees 

 Average for evergreens 



Warm 

 season. 



70 

 65 

 74 



It seems that the deciduous trees withhold more of the precipitation 

 (3 per cent) through the entire year than do the evergreens, and that 

 this percentage additional becomes 9 in the leafy season. 



Less than two-thirds of the rainfall in open fields, during this season, 

 succeeds in reaching the gauge under deciduous trees; more than three- 

 quarters reaches it under evergreens. This difference may be easily due 

 to the character of the foliage in the two cases. 



As an average from sixteen stations, and al)out 150 years of observa- 

 tion, it is found that, in the warm season. 30 per cent of the rainfall in 



