The Stem 109

little sugar, especially when new, or when it is
beginning to shoot, and soluble carboyhdrates are
required. In the Jerusalem artichoke, another tuber,
we again find inulin, though sugar, too, is always
present. The reserve material of stems is accumulated
during one year to nourish the young shoot of the
next.
In Leaves -- In the fleshy leaf bases of bulbs carbo-
hydrate is present. The onion, for instance, shows a
copious supply of sugar. In the onion, which is a
biennial, this sugar is for the production of flower and
fruit in the second year. In the bulbs of the lily and
narcissus, however, the reserve merely supplies the
young shoot till it can gather food for itself and return
what it has borrowed from the store below.
Fruits, like the apple, cherry, and blackberry, have
sugary flesh which, forming the food of birds and
other animals, provides for the distribution of the
seed. In cases moreover where the fruit falls naturally
to the ground, the fleshy material rots and forms a
supply of humus that the young seedling can use as
soon as its roots are established.
SUMMARY
Stems conduct inorganic materials to and organic
materials from the leaves, and serve to spread out the
leaves and display the flower and fruit. A dicotyledon
has epidermis to protect; cortex to conduct carbo-
hydrates from the leaves; a ring of medullary rays
alternating with vascular bundles, the latter consisting
of bast, to conduct proteins from the leaves; cambium
to provide for growth, and wood to conduct water
from the root; pith, and sometimes pith cavity in the
middle. In older stems annual rings mark the differ-
ence in growth of spring and autumn wood, pith
disappears, cortex and bast form the inner bark, and
the outer cortex forms corky bark. In monocotyledons,