212 Plant Biology 



Siy 



stored carbohydrates and proteins in bean seeds make them valuable as 

 foods. The veins (vascular bundles) of leaves conduct materials through- 

 out the leaf and are continuations of the vascular bundles of the leaf 

 petiole, stem, etc. 



The rather conspicuous flowers (Fig. 55) of the common bean are 

 irregular (bilaterally symmetrical, with petals of various sizes and un- 

 equally spaced), perfect (both stamens and pistils), and complete (all 

 four sets of flower parts). They are usually small, whitish-purple, and 

 racemose (flowers along an elongated axis). The calyx is composed of 

 four to five green sepals, more or less united. The corolla is papilio- 

 naceous (butterfly-like) and consists of four to five petals, some of which 

 may be coalesced. In those species with definitely irregular flowers, the 

 large, recurved, somewhat contorted, upper petal is called the standard, 

 the two lateral petals are called wings, and the two lower (anterior) 

 petals are fused to form the keel which may be spirally coiled. There are 

 usually ten stamens (nine of which may be united into a thin sheath 

 around the pistil while one is free) . Each stamen bears a pollen-produc- 

 ing anther at its tip. 



The female pistil is composed of a single, elongated ovary (one carpel) 

 which contains several ovules, a filamentous style, and a pollen-receiving 

 stigma. When the ovary matures, it becomes a bivalved, multiseeded 

 pod (legume). Pollen tubes are formed through the style and extend 

 from the stigma to the ovary. Fertilization occurs in the ovary, and the 

 fertilized ovules develop into the true seeds (Fig. 56) . 



The pod (legume) is linear, usually slightly curved, with two halves 

 (valves), several internal seeds, and usually with remains of the style. 

 The seeds (Fig. 56) are composed of two similar halves known as cotyle- 

 dons in which foods have been stored for use in germination of the seed. 

 There is ?io endosperm (food), as in the case of corn, but its place is 

 taken by the two cotyledons. Each seed is attached to the pod by a stalk- 

 like funiculus (fu -nik' u lus) (L. funiculus, small cord) . 



The bean seed is a dicotyledon which lacks endosperm. The seeds, _ 

 like those of other legumes (leg' um) (L. legumen, pulse or "pod"), ^ 



are developed in a legume (pod), which is the mature, ripened ovary 

 (Fig. 56). Since a ripened ovary is known as a fruit, the legume (pod) 

 is a rather special type of fruit. 



Each individual seed consists of ( 1 ) a small, prominent scar, the hilum 

 (hi' lum) (L. hilum, small), where it was attached to the pod; (2) a 



