53 



In the calculations concerning the influence of forests on the rainfall and vegetation 

 of a country, the world has suffered from a lack of scientific observations, no country 

 having for a number of years in succession employed meteorologists to make the requisite 

 observations. In this matter of late years Bavaria has moved to great purpose, and has 

 secured already a large amount of valuable data. From these I make the following 

 quotations, which if carefully read will give my readers valuable facts lately ascertained 

 by the Bavaran Government : — 



" 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 forests, but also the litter that covers the ' 

 surface, contribute largely to the retention of moisture in the earth and to the feeding of 

 springs. The total mean loss of moistnre in litter-tSovered forest soil during the months 

 from April to October inclusive, 1869, was sixty-two per cent., and in 1870, fifty-eight per 

 cent., less than in soil free from litter. If we compare these percentages with the preced- 

 ing, we find this most interesting result ; that the litter covering contributes as much to 

 the retention 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. 



" A knowledge of the amount of precipitation (rain, snow, fog, and dew) during the 

 year has a practical as well as a scientific interest, because 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 during 

 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 its vital powers decline. According to the 

 careful investigations of Hellriegel it appears, that in sandy soils and in dry regions, the 

 size of our crops depends more upon the amount and distribution of rain than any other 

 factor. Although generally a greater warmth of the air acts favourably upon the de- 

 velopment of plants, it certainly 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- 

 ripe fruit fall. But how suddenly plants will 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 

 seasons ; in fact, the growth of forest trees and their propagation is governed 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 fibre, cells and other organic parts. Starch, 

 chlorophyl, etc., are 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 enormous 

 evaporation constantly going on through the leaves, etc., during the growing season 

 especially in the day-time, which passes off into the air as an invisible vapour, and must 

 be replenished from the soil through the agency of the roots, or they wilt and die. The 

 tree is, in one sense, a stream of water, which, during the growing season is moving from 

 the fibres of the roots, through the outer body of wood into the limbs and branches and 

 into the leaves. The forests thus withdraw a great amount of water from the soil and 

 give it off as vapour. In winter the process is partially suspended, but still there is a 



