LEGUMINOS^ 



415 



two lateral ones {wings or ala), and two lower ones more or 

 less united along their ventral edges (forming the keel or 

 carina) (Fig. 172); this keel encloses the stamens and pistils. 

 In the bud, the keel is enclosed by the wings, and the wings 

 by the standard. Stamens are mostly ten in number, and 

 either all the filaments are united {monadelphous) , as in 

 Lupinus, or nine are united and one is free (Fig. 188) (diadel- 

 phous), as in clovers and alfalfa, or rarely all stamens are 

 separate (polydelphous) , as in Sophora and Thermopsis. 



Fig. 172. — Flower of Leguminosae. A, floral diagram of Vicia faba; B, 

 sweet pea flower, dissected, diagrammatic. (A after Eichler, B after Bergen 

 and Caldwell.) 



The united stamens form a tube enclosing the pistil in 

 monadelphous and diadelphous forms. There is a single 

 superior pistil; the ovary is usually one-celled, sometimes 

 two-celled by the intrusion of the sutures, as in some Astraga- 

 lus spp., or occasionally several-celled by cross-partitions; 

 there is one style, and one to many ovules. 



Fruit. — In nearly all members of the family, the fruit is a 

 legume or pod, that is, a fruit of one carpel which opens along 

 two, both the ventral and dorsal, sutures. The ventral 

 •suture of the bean or pea pod, for example, is the one along 

 which the seeds are attached. In one tribe (Hedysareas) , 



