CHAP. VII.] WALL FRUIT TREES. 171 



to protect the blossoms from the frost, but to 

 save them from the withering- effect of the sun, 

 which is more injurious to them after a frosty 

 night than the frost itself. In fact, when tender 

 trees are covered with hoar-frost, they may 

 sometimes be saved if shaded till they have 

 thawed ; but they are always killed if exposed 

 while the frost is on them to the sun. The 

 reason is, that the sap contained in the side of 

 the branch next the wall remains unfrozen, 

 while that in the side exposed to the air is 

 melted by the heat of the sun; and thus the 

 melted sap, having no proper means of escape, 

 lacerates the vessels which contain it, by its 

 sudden expansion : whereas, when both sides 

 thaw together, the sap flows Gradually away by 

 its natural channels. Bunting is preferable to 

 matting or canvas for protecting wall trees : 

 because it is thinner, and does not entirely 

 exclude the light and air ; because it is more 

 easily put up and taken down, and takes up 

 less room when stowed aw T av; and because it 

 is cheaper, four square yards costing only two 

 shillings at Edgington's, the marquee-maker. 

 Coarse cotton net, such as is manufactured at 

 Nottingham, is also found efficacious. 



Kinds of Wall Fruit Trees, 8fc. — The prin- 

 cipal fruits grown against a wall in England 

 are those containing stones ; and of these the 

 most valuable are the peach, the nectarine, and 

 the apricot. The plum and the cherry are also 

 occasionally grown against a wall, but thev are 

 most common as standards. The kernel fruits, 

 such as the apple and pear, are generally 

 standards ; the apple being very rarely trained 



