162 THE MAGAZINE OF HORTICULTURE. 



and take heed not to infringe upon any of the conditions on 

 which these sources depend. 



Most people comprehend the value of trees for timber and 

 fuel, and their advantages for shade and ornament : but their 

 agency in promoting the fertility of the soil, the humidity of 

 the atmosphere, the fullness of the streams and wells, and 

 tlie salubrity of the climate is more imperfectly understood. 

 But according as we investigate the subject, we shall be con- 

 vinced that a certain proportion of forest in every country is 

 necessary to preserve that regular supply of moisture which 

 is essential to the growth of plants and the general health of 

 vegetation ; and that while the removal of a large portion of 

 the timber, in a country which is entirely covered with forest, 

 is necessary to render it available for agricultural purposes, — 

 still, if the country be deprived of its wood beyond a certain 

 limit it will become subject to pernicious droughts, its rivers 

 and springs will be dried up, and the land rendered waste 

 and unprofitable. 



AH scientific observers acknowledge that trees in full foli- 

 age condense moisture from the vapors of the atmosphere, and 

 conduct it to the earth ; that these vapors would remain for 

 an indefinite time suspended in the atmosphere, until they 

 met some such condensing agents, and that in proportion to 

 the quantity of forest will be the amount of moisture thus 

 arrested in its progress and carried down to water the surface 

 of the soil. Not only the foliage, but the branches of trees, 

 after their leaves have fallen, have the same attraction for the 

 moisture of the air, as may be proved, whenever there is a 

 fog, by the wetness of the ground under the trees, compared 

 with that in the open plain. Trees, therefore, act the double 

 part of supplying the atmosphere with moisture, which they 

 draw up by their roots from the depths of the earth, and dis- 

 charge in an invisible form through the breathing pores of 

 their foliage ; and of wetting the surface with the moisture 

 which they draw down by condensation from the atmos- 

 phere. 



Trees are likewise, in frequent instances, the immediate 

 occasion of showers, by conducting to earth the electricity of 



