OF PLANTS. 119 



is absorbed by the buds and tender parts of the plant as 

 it trickles over them. Then at night, if this water freezes 

 it injures, if it does not destroy, the texture of the parts 

 in which it is lodged. 



Caroline. It must surely be desirable to plant such 

 trees against a wall in a southern aspect, even under the 

 inconveniences to which such a state of confinement sub- 

 jects them. 



Mrs. B. It is attended with several advantages, which, 

 in the initiation of tropical plants to our climate, often 

 more than compensate the injury resulting from confine- 

 ment. A southern wall not only affords shelter from the 

 north wind, but becomes a source of heat, by the trans- 

 mission of the sun'.s rays to the plant. 



Emily. The white walls of France and Switzerland 

 must reflect a great deal of heat ; but I should not have 

 supposed that our brown brick English walls would have 

 produced much effect, for they must absorb more heal 

 than they reflect. 



Mrs. B. The rays, whether reflected or absorbed by 

 the wall, are alike beneficial to the tree planted against 

 it ; for no sooner does the temperature of the wall become 

 elevated by the absorption of heat than it radiates this 

 heat, which is thus transmitted to the tree in contact with 

 it. 



The injurious effects of the captivity of the branches 

 must, however, be taken into consideration ; for, besides 

 the salubrious exercise which free access of air affords to 

 a plant, this agitation augments the power of evaporation 

 a power which it is very desirable to encourage, as 

 it is necessarily diminished in a climate of a lower tem- 

 perature than that in which the plant was placed by Na- 

 ture , especially in England, where the atmosphere is 

 impregnated with moisture. It is owing to this circum- 

 scribed power of evaporation that wall-trees are less hard 

 in their texture, and contain less carbon, than those which 

 grow freely. 



667. What will be the effect of planting trees upon the south side of a 

 walll 668. What comparison does Emily make between the walls of 

 France and Switzerland and those of England 1 ? 669. What is the re- 

 ply of Mrs. B.1 670. What is said of the effect of confinement to 

 trees against a walll 671. Why are such trees less hard in their tex- 

 ture* 



