138 DICOTYLEDONS 



each. The pea is a climbing annual with pinnate leaves 

 (fig. 59) and large green persistent stipules (n) ; some of the 

 leaflets are converted into tendrils {6r). Inflorescences 

 axillary : capitulum in the clover ; peculiar, two-flowered in 

 the pea. Flowers (figs. 96, 97) median-zygomorphic, irregular, 

 9 , cyclic, perigynous. Sepals five, combined to form a five- 

 toothed cup. Petals five, polypetalous, irregular. The 

 posterior petal {sd) is the largest, and is termed the standard 

 (vexillum) ; the two lateral petals (w) are termed the wings 

 («/«) ; whilst the two anterior petals (A), which have separate 

 claws, cohere by their blades, and form the boat-shaped 

 keel (carina). The jestivation (fig. loi) is descending-imbricate 

 (see page 73). Stamens (fig. 87) ten, weakly perigynous. 

 The single posterior stamen (pa) is separate, but the filaments 

 of the nine others cohere to form a tube (an. t), which is open 

 only along its posterior face (as well as at the summit). 

 Though the ten stamens represent two whorls of five each, all 

 ten are inserted at the same level on the receptacle. The 

 stamens lie hidden inside the keel, and they in turn conceal 

 the single ovary. The base of the inner face of the staminal 

 tube acts as a nectary. Carpel one, superior ; ovary (ov) one- 

 chambered, bearing a double Une of ovules on the parietal 

 placenta; style one; stigma (sg) simple. Fruit (fig. 119), a 

 legume. Seeds non-endospermic. Pollination. — Like the 

 flowers of all the Papilionaceas, these flowers are specially con- 

 structed for pollination by means of bees. The bee alights on 

 the flower in such a way as to use the alae as a platform. This 

 depresses the alae, which in turn drag the keel (carina) down. 

 In this manner the upwardly directed stigma and the pollen 

 inevitably come into contact with the under-surface of the bee's 

 body. The bee thrusts its tongue into the slit on the upper 

 (posterior) face of the staminal tube and sips the honey which 

 accuinulates between the base of the ovary and the base of the 

 staminal tube. When the bee flies away, the two alae and the 

 keel rise up again and assume their former positions. The bee, 

 visiting flower after flower, may thus effect cross-pollination. 

 The flowers may self-pollinate themselves. In these flowers we 

 may note : (i.) How completely the alae and carina protect the 

 honey and pollen from rain and marauding insects. (ii.) The 

 honey can only be reached from above (from the posterior face 

 of the staminal column), (iii.) The alae, when forced down, 



