468 STRUCTURE AND LIFE HISTORIES 
peculiarly modified corolla called papilionaceous, from its 
fancied resemblance to a butterfly (Fig. 350). 
2. Casalpinioidea, containing the red-bud (Cercis), true 
or honey-locust (Gleditsia), wild senna (Cassia marilan- 
dica), and others, whose flowers are only imperfectly or 
not at all papilionaceous (Fig. 351). 
3. Mimosoidea, containing the acacias, sensitive plants 
(Mimosa), and others having flowers with a regular corolla. 

^ *V| " -iasiMBi^E^S^sas^^MHS^^^ 
FIG. 352. Legume of the edible pea (Pisum sativum). a, anther; c, 
calyx; st, stigma. 
calyx; st, stigma. 
Flowers that are bilaterally symmetrical, like the papilio- 
naceous flowers, are called zygomorphic. Such flowers as 
the buttercup, rose, and others may be divided into equal 
halves by an infinite number of planes of symmetry. 
The one feature that characterizes all three of the sub- 
families 1 is the simple pistil, composed of one carpel, and 
enlarging greatly in fruit (as in peas and beans) to form a 
legume (Fig. 352); whence the name of the family. 
The structure of the papilionaceous corolla is illustrated 
in Fig. 350. The upper and largest petal, stands erect, 
1 By some authors each group, designated above as a sub-family, is 
considered as a separate family. 
