FLOWERS AND FRUIT > 25 
The last of the four kinds of parts is found in the center 
of the flower, and is called the pistil. Itis 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 for- 
mation 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. 
Kinps oF FLOWERS.—When the pelnls. & are entirely 
separate from each other, as in the 
Apple-blossom, the flower is said to be gas 
polypetalous ; when they grow together © 
more or less, as in the Catalpa (Fig. 10), € 
monopetalous ; and when the corolla is ~ Fig. 10. 
wanting, as in the flowers of the Oak, apetalous. 
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, ete.; in that 
case the plant is said to be monecious, and all trees of 
this kind produce fruit. Sometimes, however, the stam- 
inate and pistillate flowers are on separate trees, as .in 
the Willows, which are diwcious; and then only a por- 
tion of the trees—those with pistillate flowers— produce 
fruit. 
