200 THE KITCHEN-GARDEN, [chap. vii. 
the heat necessary to mature their fruit, by 
reflecting the sun’s rays back upon it; and 
by giving out to the fruit during the night 
the heat they have absorbed during the day. 
They are also useful in sheltering the plant 
from cold winds; and in preventing the 
branches from bruising each other in violent 
storms. This being the use of walls, it is 
evident that only those trees should be 
trained against them that require protection; 
and the south and south-east walls being 
warmer than the others, it is equally evident 
that only those trees should be trained 
against these walls, that require a great deal 
of heat to mature their fruits. There are 
some fruits, such as the apple, which too 
much heat renders mealy and insipid; and 
these would obviously be injured instead of 
improved by a south, or south-east wall; 
while other fruits, such as the peach, could 
not produce good fruit in our climate with¬ 
out one. Before planting trees against the 
walls of a garden, it will thus be necessary 
to select the trees proper for each wall; and 
as some of the finer kinds will be several 
years before they attain a sufficient size to 
