452 



THE ROSALES 



make a very easy transition from the regular flower of the plum 

 to the highly modified flowers of the Pea family. 



(b) The Pea Family, Papilionaceae. — The Pea family (Fig. 

 316) is the highest of the rose order and the largest family, with 

 one exception, of all the angiosperms, comprising over 11,000 

 species. Here we find the same type of flower as in the redbud. 



Fig. 315. Development of the irregular type of flower in the rose order: 

 A, regular flower of the honey locust {Gleditsia). At left staminate flower. 

 At right pistillate with single pistil, c, which develops into long flat pod, s. 

 rudimentary stamens. B, flower of Cassia, showing slightly irregular corolla. 

 C, section of flower — s, stamen; c, pistil. D, the fruit or pod. E, irregular 

 flower of redbud (Cercis) — c, calyx; k, keel enclosing stamens and pistil; w, 

 wings which arch over the standard, s. F, corolla removed, showing the ten 

 stamens surrounding the simple pistil, c. 



The standard in this family, however, incloses the wings and 

 the stamens, usually ten in number, may be distinct as noted 

 above or united by their filaments into a sheath about the soli- 

 tary pistil; more frequently a single stamen remains free, an 

 arrangement called diadelphous (two brotherhoods). This type 

 of flower is called papilionaceous from its fancied resemblance 



