i666 A TEXTBOOK OF THEORETICAL BOTANY 



The calyx is gamosepalous and five-toothed or sometimes bilabiate, 

 caused by a partial split of the tube into a two- and a three-toothed part. 



The corolla is polypetalous, composed of five petals which are regu- 

 larly imbricated in a characteristic descending manner in the bud (Fig. 1527). 

 These petals are all dissimilar and have received separate names. The 

 adaxial petal is large and forms the standard or vexillum ; the two lateral 



Fig. 1527. — Pisiim sativum. Longi- 

 tudinal section of flower 

 showing arrangement of corolla 

 parts in relation to the sex organs 



ones form the wings or alae and lie more or less parallel to each other, 



while the two lower petals which lie internal to the wings and are united 



by their lower margins, form the keel or carina. 



The androecium consists of ten stamens which may be all free or 

 either monadelphous, as in Cytisus, or diadelphous, as in Lathyrus, where the 

 posterior stamen is free. The anthers mostly open lengthwise. 



The gynoecium is monocarpellary and the ovary superior and uni- 

 locular. The ovules are indefinite in number, anatropous or campylotropous, 

 alternating in two rows, with marginal placentation. 



The fruit is usually a legume or more rarely a lomentum. 



The seed is large and non-endospermic, the embryo consisting of two 

 large hemispherical or flattened cotyledons, with a generally superior or 

 ventrally placed radicle. 



The family is the second largest of the Dicotyledons and contains about 

 500 genera and over 11,000 species. It forms a very characteristic and 

 natural group with world-wide distribution. There are few anatomical 

 features which are characteristic of the whole family. Internal secretory 

 systems of various kinds are generally present. Anomalous stem structure 

 is associated with liana types and consists mainly of the development of 

 phloem tissue in the secondary wood, e.g., Phaseohis, or the development of 

 successive rings of vascular bundles as in Wistaria. On account of its very 



