UNISEXUAL FLOWERS 13 
Flowers having the four sets of organs, as shown in Figure 2, 
are called complete flowers to distinguish them from incomplete 
flowers, that is, flowers in which some of the 
organs are lacking. The organs are gener- 
ally arranged in a circular fashion around 
the receptacle, and are characterized as be- 
ing in cycles or whorls. In some flowers a 
part or all of the perianth is lacking. In 
the Buckwheat, as shown in Figure 3, only 
one whorl surrounds the stamens and pistil, 
and it is evident that this flower does not 
have both calyx and corolla. In such cases, 
the petals are considered missing and the 
flower is said to be apetalous (‘‘ without 
petals’). Often instead of being composed Fic. 7. — Section 
of entirely separate petals (polypetalous), ‘b7oush 2 Hower of the 
y , P P poe. » Peach. There is but 
the corolla is a tube or funnel-shaped struc- one pistil (p), but many 
ture, which appears to be composed of united stamens (s). Much en- 
petals (gamopetalous), separate only at the lrged. 
top. (Fig. 4.) The flowers of the Tobacco Plant, Pumpkins, 
Squashes, and Water- 
melons are examples of 
gamopetalous flowers. 
In some cases, as in the 
Tobacco, Clover, and 
some other plants, the 
sepals seem to have 
joined into one structure 
(gamosepalous), forming 
a tube- or cup-like calyx. 
(Fig. 4 and 5.) Flowers 
also differ in the essential 
organs contained. 
Fic. 8.— Section through an Apple flower  Unisexual Flowers. — 
showing the compound pistil composed of five Flowers having both sta- 
carpels. The five carpels (a) are free above mens and pistils are 
but joined below. c, corolla; s, stamens; 7, known as perfect or bisex- 
calyx. Much enlarged. 
ual flowers. In some 
plants, the stamens and pistils occur in different flowers, in which 
case the flower having stamens only is called a staminate flower, 
