The Leaves. 79 
leaves are, in most plants, so arranged as to best expose 
them to light, i. e., in thin, more or less horizontal plates, 
which are strengthened, and at the same time supplied with 
water, by a network of vascular bundles (68) connecting 
with the stem. They are protected by the epidermis (62), 
but have access to air through the stomata (66). 
Each leaf, like the stem and root, is developed from one 
or more growing points (67), one of which forms the ter- 
minus of each lobe or division of the leaf. Cell division in 
the leaf is confined to the near vicinity of the growing 
points, heuce an injury to the older part of the leaf is not 
repaired further than by the formation of callus (73) over 
the wounded parts. 
122. The Cultivator Should Provide for Normal 
Leaf Development. Since the protoplasm of the plant is 
nourished by assimilated food (59), and since assimilation, 
in most plants, takes place almost wholly in the leaves, 7t is 
of first importance that the plant be so cared for as to pro- 
mote normal leaf development. Without this, good crops are 
impossible. The plants must be grown far enough apart so 
as not to unduly shade each other; insects and fungi must 
not be permitted to prey upon them when it is possible to 
prevent it; and the leaves must not be needlessly removed 
or injured. 
123. How Far Apart Should Plants be Grown? 
When the finest developed plants, or parts of plants, as 
fruits, flowers, leaves, stems or roots is desired, the plants 
should not be grown so near together as to interfere with 
each other's leaf or root development. But when the largest 
crop from a given area is of more importance than the 
development of the individual plant, as with grain crops, 
