50 



"by his investigations that in the lucerne the amount of water evaporated in the sun is 

 ■four times greater than it is in the shade. The difference of evaporation in the two con- 

 ditions is with this plant considerably greater than with corn. In some plants, as in the 

 willow, it is, however, very slight. This is no doubt the reason why some plants will 

 thrive better in the shade than others. Transpiration is also diminished by a fall of 

 temperature and an increase in the humidity of the atmosphere. "With the decrease of 

 warmth and the lessened influence of light, the transpiration of plants becomes less in 

 autumn, and finally stops entirely, causing the falling of the leaves. The evaporation 

 •of the leaves is very slight in a damp* or foggy atmosphere, and when the leaves are wet 

 by dew or rain. In the damp air of our hot-houses, and under glass vases, often placed 

 over weakly plants, the amount of evaporation is very slight. It is correspondingly 

 lessened in the shade of trees in the cool and damp air of dense forests and under arti- 

 £cial coverings. 



" In order that the leaves of plants may remain fresh and plump, as much water 

 must be taken up by the small fibres of the roots as is lost by transpiration. A constant 

 •circulation of water is going on from the roots through the trunk to the branches, and 

 through these and the stems into the leaves. The plants remain in a normal condition 

 whenever the supply of water by the roots and loss by evaporation correspond. Under 

 «ome circumstances it will occur that the supply of water received through the root is 

 ^eater than the loss through the leaves, or that the loss is greater than the supply. 

 Instances of the former case are presented in the plant which during the night evaporates 

 less water than it receives from the ground through the roots. The surplus is deposited 

 •on the leaves m small drops, which, upon examination, may be found early in the morning 

 ■even in the hot-houses, which precludes the idea that they are gatherings of dew. Another 

 instance is shown in our deciduous trees in autumn after the fall of the leaves, when, 

 irom a relatively warm soil the roots maintain their activity, and continue to receive 

 moisture from the soil, which will remain in the body of the tree, as the organs of evap- 

 oration are gone. This explains the reason why there is a greater amount of water in the 

 body of the tree in autumn than there is in summer. It is of tener the case, however, that 

 the amount of water lost is greater than that received, which occasions in herbage and 

 young plants a withering of the leaves. Larger trees are not materially affected by this 

 interruption, as the body of the tree acts as a reservoir of water, from which the trees are 

 supplied for some time. The withering and drying up of plants is not always the result 

 of an insufficient amount of moisture in the soil, but it may occur when, in consequence 

 •of a lack of activity in the roots the absorption of water from soil is not proportioned to 

 the loss by transpiration." 



Here is a word from California. The Nevada Enterprise says : — " It will be but a 

 very short time before we shall be able to observe the effect that stripping the fine forests 

 irom the sides and summit of the Sierras will have on the climate of this State and Cali- 

 iornia. In a very few years every accessible tree, even to such as are only of value as 

 £rewood, will be swept from the mountains. Even now this has been done in some 

 places. It is to be hoped that a new growth of pines or timber trees of some kind may 

 spring up on the ground that has been cleared, but we do not hear that any such growth 

 has yet started. 



" Already' one great change has occurred that is evident to the most ordinary observer, 

 which is the speedy melting away of the snow on the mountains. It now goes off at once, 

 in a flood, with the first warm weather of spring, whereas formerly, lying shaded and 

 protected by the pines and other evergreen trees, it melted slowly, and all summer sent 

 •down to the valleys on both the eastern and western slopes of the Sierras constant and 

 •copious streams of water. Instead of a good stage of water in our streams throughout 

 summer, as in former times, there is a flood in the spring, and when this is passed by our 

 , rivers speedily run down, and being no longer fed from the mountains, evaporation leaves 

 their beds almost dry when the hot weather of summer comes on. 



" The mountains being stripped of their trees, there will be nothing to shade the 

 Tocks and earth, and both will absorb a sufficient amount of heat from the rays of the sun 

 during the fall, and even until far into the winter, to melt any light snow that may occur. 



