e cotyledon
or seed leaf, and the leaves from the first are alternate. As a rule
the embryo is very small and surrounded by abundant endosperm.

The most thoroughly typical members of the sub-class are the lilies
and their relatives. The one selected for special study here, the
yellow adder-tongue, is very common in the spring; but if not
accessible, almost any liliaceous plant will answer. Of garden
flowers, the tulip, hyacinth, narcissus, or one of the common lilies
may be used; of wild flowers, the various species of _Trillium_
(Fig. 83, _A_) are common and easily studied forms, but the leaves are
not of the type common to most monocotyledons.

The yellow adder-tongue (_Erythronium americanum_) (Fig. 81) is one of
the commonest and widespread of wild flowers, blossoming in the
northern states from about the middle of April till the middle of May.
Most of the plants found will not be in flower, and these send up but
a single, oblong, pointed leaf. The flowering plant has two similar
leaves, one of which is usually larger than the other. They seem to
come directly from the ground, but closer examination shows that they
are attached to a stem of considerable length entirely buried in the
ground. This arises from a small bulb (_B_) to whose base numerous
roots (_r_) are attached. Rising from between the leaves is a slender,
leafless stalk bearing a single, nodding flower at the top.

The leaves are perfectly smooth, dull purplish red on the lower side,
and pale green with purplish blotches above. The epidermis may be very
easily removed, and is perfectly colorless. Examined closely,
longitudinal rows of whitish spots may be detected: these are the
breathing pores.

[Illustration: FIG. 81.--_A_, plant of the yellow adder-tongue
(_Erythronium americanum_), x 1/3. _B_, the bulb of the same, x 1/2. _r_,
roots. _C_, section of _B_. _st._ the base of the stem bearing the
bulb for next year (_b_) at its base. _D_, a single petal and stamen,
x 1/2. _f_, the filament. _an._ anther. _E_, the gynoecium (pistil), x 1.
_o_, ovary. _st._ style. _z_, stigma. _F_, a full-grown fruit, x 1/2.
_G_, section of a full-grown macrosporangium (ovule), x 25: i, ii, the
two integuments. _sp._ macrospore (embryo sac). _H_, cross-section of
the ripe anther, x 12. _I_, a single pollen spore, x 150, showing the
two nuclei (_n_, _n'_). _J_, a ripe seed, x 2. _K_, the same, in
longitudinal section. _em._ the embryo. _L_, cross-section of the
stem,