18 QUINCE CULTURE. 
cut back or broken off by accident, or when even the 
whole head of the tree has been removed. In avery vig- 
orous tree it is quite common to have the buds push 
their threefold development simultaneously; the central 
growth bearing the blossom, and those on either side of 
it only making wood-growth. Occasionally two of the 
three bloom together. By observing the position of 
the buds along a branch, in going the length of five buds 
you can so prune as to give any desired direction to the 
new growth, and thus form a symmetrical tree. 
The leaves, with their stipules, form the foliage of the 
tree, and seem to serve much the same parpose for it that 
the lungs of animals do for them. Leaves not only give 
beauty to the tree, but are necessary to its existence. 
They are formed of a series of veins, between which is 
the cellular tissue or parenchyma, which consists of 
numerous cel/s of various forms, with air spaces between 
to increase the surface exposed to the air and sunlight. 
There are about 25,000 of these breathing pores in each 
leaf, through which moisture and air are received, and 
vapor and carbonic acid given off. By this process the 
sap in the leaves is thickened, and the material of woody 
fiber elaborated. The wood of trees is chiefly carbon, 
which the leaves have absorbed from the air. Their ni- 
trogen comes from the combined influence of the air, the 
sun’s light and heat, the humus of the soil, and the action 
of potash. Analysis of the ashes shows that a very small 
part of the constituents come from the soil. The air 
is an abundant storehouse of exhaustless capacity, full 
of the materials of plant growth, to which each culti- 
vator possesses a key. Every man and air-breathing 
animal on earth is helping to keep this atmospheric 
storehouse filled with the material of plant growth 
by every breath exhaled ; and so all animated creation 
is at work for the tiller of the soil. Not only are 
the leaves the laboratory of the growing wood, but 
