lled the _pistil_. It is this part which forms the
fruit and incloses the seed.

The stamens and the pistil are the _essential_ organs of a flower,
because they, and they only, are needed in the formation of seeds. The
pollen from the stamen, acting on the pistil, causes the _ovules_ which
are in the pistil to grow into _seeds_.

The calyx and corolla are called _enveloping organs_, since they
surround and protect the essential parts.

The pieces of which the calyx is composed are called _sepals_. The
Apple-blossom has five sepals.

The pieces that compose the corolla are called _petals_.

KINDS OF FLOWERS.--When the petals are entirely separate from each
other, as in the Apple-blossom, the flower is said to be _polypetalous_;
when they grow together more or less, as in the Catalpa (Fig. 10),
_monopetalous_; and when the corolla is wanting, as in the flowers of
the Oak, _apetalous_.

[Illustration: Fig. 10.]

When all sides of a flower are alike, as in the Apple-blossom, the
flower is _regular_; when one side of the corolla differs from the other
in color, form, or size, as in the Common Locust, or Catalpa, the flower
is _irregular_.

In trees the stamens and pistils are often found in separate flowers; in
that case the blossoms containing stamens are called _staminate_, and
those containing pistils _pistillate_; those that contain both are
called _perfect_. Staminate and pistillate flowers are usually found on
the same tree, as in the Oaks, Birches, Chestnut, etc.; in that case the
plant is said to be _monoecious_, and all trees of this kind produce
fruit. Sometimes, however, the staminate and pistillate flowers are on
separate trees, as in the Willows, which are _dioecious_; and then
only a portion of the trees--those with pistillate flowers--produce
fruit.

ARRANGEMENT OF FLOWERS.--Flowers, either solitary or clustered, grow in
one of two ways; either at the end of the branches, being then called
_terminal_, or in the axils of the leaves, then called _axillary_. The
stem of a solitary flower or the main stem of a cluster is called a
_peduncle_; the stems of the separate blossoms of a cluster are called
_pedicels_. When either the flowers or the clusters are without stems,
they are said to be _sessile_.

_Clusters with Pedicellate Flowers._

_Raceme_, [Illustration] flowers on pedicels of about equal length,
scattered along the entire stem. Locust-tree.

_Corymb_, [Illustration] like a raceme exc