266 BOTANY. 
scented as well as showy, their regularity of form prevents 
perfect cross-pollination. However, as the flowers are 
generally in clusters, it usually happens that the pollen 
from one flower is carried to the stigmas of another. The 
attractiveness of the flowers is such that through the visits 
of great numbers of insects the large amount of pollen is 
pretty well distributed upon other stigmas. 
539. In the nearly related Leguminous Plants, as beans, 
peas, clover, lupines, etc., the perianth is not regular. 
There are three forms of petals in each flower, viz., one 
Fia. 145,—Flower of Dead-nettle, side view and vertical section. Magnified. 
large broad one, the “banner,” two lateral ones, the 
“wings,” and two anterior ones which together form the 
“keel.” These all together form a structure enclosing the 
stamens and pistil in such a way that an insect cannot get 
any of the nectar at the base of the corolla without setting 
free some of the pollen, which adheres to the hairs of its 
body and is thus carried to the stigma of some other flower. 
540. In the Gamopetale the union of petals into a tube 
serves to compel insects to visit the flower in one way only. 
In the Mints (Fig. 145) the flower is two-lipped, the broader 
