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fall on the forest, it soaks into the spongy bed of the ground, renewing that deposit of 

 moisture which in winter the snow had kept fully supplied. The snow was kept there in 

 the partial shade of the branches, the water melting from it kept by the peculiarities of the- 

 surface — ^that soil of the forest already described, with its roots, logs, and inequalities — 

 till spring was advanced and yet a good supply of moisture remained for summer. Then 

 comes the rain, and is stored like the former, while night after night the dew adds its. 

 share and assists in maintaining the great forest bank, on which the thirsty fields for- 

 miles round perpetually draw, and perpetually, too, return back honestly that moisture 

 which they have borrowed. So long as the forest is left in fair amount, field and wood'' 

 act, in reference to supplies of water, like a great self -regulating and compensating 

 machine. But when we destroy one part of the engine, we do not find it to work (and, 

 no wonder) so beneficially or so smoothly as before. 



The moisture in forests is further increased by that obtained from mists, which are». 

 in fact, clouds forming near the earth. The particles in these are not yet large enough to 

 form drops of rain, and are, till further condensed by change of temperature, kept apart , 

 by the nature of their present support in the air. But, as when one is passing through 

 a fog, the water collects on the beard and on the clothes, so with trees, though the 

 particles of moisture in the fog be so small that a heated wind (rising the temperature, 

 which, as before explained, renders the air capable of taking in more vapour of water)' 

 might have absorbed and carried it all away again. Yet all which touch the innumerable 

 leaves stay there, coalesce there, run together, and fall to the ground. 



It must be remembered with relation to dew on forest leaves, that there is a vast 

 transpiration frequently goiag on from them, which must interfere somewhat with the 

 deposit of dew on the same leaf. This transpiration, which will be shortly described, 

 takes place while the tree is warm, that is, uncooled by radiation, and continues till far 

 on in the night. It becomes more feeble, as various writers state, from the leaves of ' 

 plants cJf all species, when covered with dew. This is inevitable; the leaf must cool to 

 form dewj it is before cooling that transpiration is most active. It must also be remem- 

 bered that except in case of leaves such as water-lilies, which float, the openings — the 

 stomata — are largely on the under surface, thereby interfering less with the operation of 

 dew-forming. 



The reader will find it worth while to study these three or four paragraphs by an 

 acute writer relating to the same subject: — 



"The clouds occasionally seen over woods, while the atmosphere around is com- 

 pararatively clear, are consequent on the condensation of the humidity occasioned by the 

 evorporation from the leaves." 



" There is always moisture existing in the atmosphere ; it is reckoned one of its con- 

 stant constituents, but it varies in quantity. The quantity is minute compared with that 

 of the oxygen and nitrogen of the air; but it is never absent. There it is, on the hio-hest 

 mountain and in the deepest mine; on the ocean's surface and on the dry land a thousaudj 

 miles away. " 



" The quantity of moisture passing into the atmosphere from the leaves of a forest 

 in active vegetation must be considerable. Calculate the number of storriata, or stomates 

 on a leaf, multiply this by the number of leaves on a branch, the product by the number ■ 

 of such branches on a tree, and the product of this by the total number of trees in the 

 clump, or the total number of trees in the forest, and the final product will indicate the - 



