THE FLOWER | 207 
occur in different flowers, both kinds of flowers may be on the 
same plant (monecious plants) (Figs. 208, 209), as in the cases 
| of corn and the castor-oil plant, or they 
may be on different plants (diwctous plants) 
(Figs. 210, 217). 
Perianth. While the stamens and pistils 
are the essential parts of a flower, they 
are usually surrounded by thin, expanded 
structures which collectively constitute the 
Fie. 205. Cross sec. Dereanth. In a complete flower the perianth 
eeeten ovary of is divided into an interior part, or corolla, 
Hibiscus, showing five ®0d an outer part, or calyx (Figs. 202, 203). 
cavities or cells con- Corolla. The corolla may be composed of 
taining ovules. (x10) a number of separate thin units, the petals 
(Hig. 211), which are white or bright- 
colored, or of a more or less tubular (Fig. 212), bell-shaped, 
or funnel-shaped structure (Fig. 213) with lobes which repre- 
sent the petals. The function of a conspicuous, bright-colored 


Fig. 206. Cross section of anther, with pollen grains and pollen sac. (x 85) 
Below, two types of stamens 
corolla seems to be to attract insects or, sometimes, small birds 
which carry pollen from one flower to another. Bright-colored 
or conspicuous flowers are usually pollinated by insects. 
