LEGUMINOSiE 



417 



Flowers small, many in a cluster. 



Flowers in slender, spike-like racemes, Mdihlus (sweet clover). 

 Plowers in heads or short spikes, Medicago (alfalfa and other medicks). 

 Flowers medium to large, few in a cluster. 

 Pods smooth, mostly large. 



Keel of corolla spirally coiled (Fig. 176, A), Phaseolus (bean). 

 Keel of corolla merely incurved, Vigna (cowpea). 

 Pods hairy, small, Soja (soy bean). 

 Leaves pinnate, with two pairs of leaflets, Arachis (peanut). 



PISUM (Pea) 



Description. — The plants are herbaceous trailers or 

 climbers with hollow stems. The leaves are pinnately 

 compound, with one to three pairs of leaflets, the terminal 

 one, and in some cases the upper lateral ones, modified as 

 tendrils, which are sensitive and prehensile; the stipules are 

 large and leaf-like (Fig. 19). The inflorescence is a few- 

 flowered axillary raceme. The 

 flowers are either white or pur- 

 plish, diadelphous, and bear a 

 single pistil with the style 

 bearded on the inner side (Fig. 

 173, A). The pea is capable of 

 self-fertilization although it 

 may sometimes be cross-ferti- 

 lized. The mature fruit is a 

 typical legume with a number 

 of smooth or wrinkled, usually green or yellow seeds 

 ("peas")- Gregory studied the histology of round and 

 wrinkled peas. In round peas, including the indented sugar 

 peas, the central tissue in the cotyledon leaves is filled with 

 very large starch grains. In wrinkled peas, on the other 

 hand, this region of the cotyledons has starch grains which are 

 usually compound, the component parts being about one-half 

 the size of the grains in smooth peas. The seed coat is 

 27 



Fig. 173. — A, style and stigtna of 

 Vicia; B, same of Lathryus. 



