ces might develop into a leaf, is capable of developing into a
petal, a stamen, or a pistil, according to the requirements of the plant,
but no actual metamorphosis takes place. Sometimes, instead of developing
into the form we should normally find, the organ develops into another
form, as when a petal stands in the place of a stamen, or the pistil
reverts to a leafy branch. This will be more fully treated under flowers.
The study of the different forms in which an organ may appear is the study
of _morphology_.

1. _Forms of Stems_.--Stems may grow in many ways. Let the pupils compare
the habits of growth of the seedlings they have studied. The Sunflower and
Corn are _erect_. This is the most usual habit, as with our common trees.
The Morning Glory is _twining_, the stem itself twists about a support.
The Bean, Pea and Nasturtium are _climbing_. The stems are weak, and
are held up, in the first two by tendrils, in the last by the twining
leaf-stalks. The English Ivy, as we have seen, is also climbing, by means
of its aerial roots. The Red Clover is _ascending_, the branches rising
obliquely from the base. Some kinds of Clover, as the White Clover, are
_creeping_, that is, with prostrate branches rooting at the nodes and
forming new plants. Such rooting branches are called _stolons_, or when
the stem runs underground, _suckers_. The gardener imitates them in
the process called layering, that is, bending down an erect branch and
covering it with soil, causing it to strike root. When the connecting stem
is cut, a new plant is formed. Long and leafless stolons, like those of
the Strawberry are called _runners_. Stems creep below the ground as well
as above. Probably the pupil will think of some examples. The pretty
little Gold Thread is so named from the yellow running stems, which grow
beneath the ground and send up shoots, or suckers, which make new plants.
Many grasses propagate themselves in this way. Such stems are called
_rootstocks_. "That these are really stems, and not roots, is evident
from the way in which they grow; from their consisting of a succession of
joints; and from the leaves which they bear on each node, in the form
of small scales, just like the lowest ones on the upright stem next the
ground. They also produce buds in the axils of these scales, showing the
scales to be leaves; whereas real roots bear neither leaves nor axillary
buds."[1] Rootstocks are often stored with nourishment. We have already
t