RESULTS OF COMPARATIVE OBSERVATIONS : BAVARIA. 2 17 



Thus, by direct observation, it being; shown, with certainty, that the 

 evaporation in forests covered with litter is very much less than that of 

 naked soil under like circumstances, there can be no longer a doubt 

 that not only the forests, but also the litter that covers the surface, con- 

 tribute largely to the retention of moisture in the earth and to the feed- 

 ing of springs. The total mean loss of moisture in litter-covered forest- 

 soil during the months from April to October, inclusive, 1869, was G2 

 per cent., and in 1870, 58 per cent., less than in soil free from litter. If 

 we compare these percentages with the preceding, we find this most in- 

 teresting result: that the litter covering contributes as much to the re- 

 tention of moisture in the soil as forests themselves. In very rainy 

 seasons this influence is less than in dry years. From this it is seen 

 how important it is to retain a protecting covering of moss or leaves on 

 the soil, especially upon mountain slopes, where, without litter, or even 

 without woods, but very little water penetrates the soil, the water for 

 the most part running off into the valleys. 



As these differences are most in warm weather, so they must be great- 

 est in warm countries. 



Bain-fall in the open fields and in the forests, and the influence of forests 

 upon the amount of rain. 



A knowledge of the amount df precipitation (rain, snow, fog, and 

 dew) during the year has a practical as well as a scientific interest, be- 

 cause not only is the height of mean water in our rivers governed by 

 the amount of rain and snow, but also the yield of our crops is largely 

 dependent upon the amount of moisture in the earth. Each plant, dur- 

 ing its life, uses a considerable amount of water as compared with its 

 weight, and this is derived mainly from the soil. In great drought the 

 plant either dies, or is developed but poorly, forming few roots and few- 

 leaves and seeds. In fertilized soils it may thrive better, but without 

 sufficient moisture and its vital powers decline. According to the careful 

 investigations of Hellriegel it appears that, in sandy soils and in dry re- 

 gions, the size of our crops depends more upon the amount and distri- 

 bution of rain than any other factor. Although generally a greater 

 warmth of the air acts favorably upon the development of plants, it cer- 

 tainly does no service unless the soil receives a corresponding amount 

 of rain. 



The action of the water begins with germination, and continues till the 

 formation of the fruit. In the early summer months the grass will 

 wither in the meadows, the herbs and young plants will dry up, the 

 leaves and blossoms of trees will droop, and the half-ri[)e fruit fall. But 

 how suddenlj' will plants revive when a long-delayed rain falls on the 

 arid earth ! The forester knows from experience the injuries caused by 

 drought. He knows that forest vegetation demands a certain minimum 

 of yearly precipitation, which must be relatively greater in warmer and 

 drier climates and soils. He also knows that the growth of wood is 

 greater in moist and moderately warm years than in hot and dry sea- 

 sous ; in fact, the growth of forest trees and their propagation is gov- 

 erned in a very large degree by the distribution of moisture. 



The great claims which trees make upon the moisture in the soil are 

 explained by the circumstance that they contain a large amount of 

 water, which forms the principal part of their sap, and a part of the 

 wood fiber, cells, and other organic parts. Starch, chlorophyl, «&c., arc 

 saturated with water. It is by its agency that the functions of nutrition 

 and growth are carried on. This want Is greatly increased by the 



