168 GENERAL BOTANY 



watches a bee seeking for nectar, or pollen, in its flowers. The 

 bee will be seen to go rapidly from one flower to another on the 

 inflorescence, probing for nectar at the base of each flower and 

 so dusting its body abundantly with pollen. When one inflor- 

 escence is exhausted, the bee moves to another and repeats the 

 process. It is quite evident that abundant close-pollination will 

 thus be effected by such a bee between flowers of the same plant, 

 and that cross-pollination will be effected if the bee visits succes- 

 sively inflorescences borne on different plants. Moreover, many 

 more pollinations will occur than could possibly be secured if 

 the flowers were borne separately from the axis of the ordinary 

 leaves of the plant. In discussing devices for insuring abundant 

 pollination the inflorescence is therefore of prime importance as an 

 aid in securing frequent close-pollination and cross-pollination. 

 The head of the common white and red clovers and the large 

 flower clusters of the sweet pea and bean are other familiar in- 

 stances of inflorescences in the pea family which are of advantage 

 in securing cross-pollination of the flowers of these species. 



Pollination devices in papilionaceous flowers. Structure of the 

 flower. The flowers of the pea family are very highly specialized, 

 and some are adapted to self-pollination and some to cross- 

 pollination. They are usually called papilionaceous flowers, from 

 their fancied resemblance to butterflies of the genus Papilio. The 

 general relations of the floral parts as they appear in the 

 garden pea are illustrated in Fig. 89. The perianth is com- 

 posed of both calyx and corolla, each having five parts desig- 

 nated respectively as sepals and petals. The calyx is nearly 

 regular, but the corolla is very highly modified and irregular. 

 The largest petal is called the standard, since it projects promi- 

 nently, like a standard, from the rest of the flower. The standard 

 petal overlaps two lateral petals, or wing petals, and these inclose 

 two united keel petals, which together form the boat-shaped keel. 

 In the normal condition of the flower the stamens and pistil are 

 inclosed and concealed from view by the keel. In Fig. 89, c, 

 a flower is shown in which the petals on one side, including 

 one half of the keel, have been removed so as to expose the 

 stamens and the pistil in their natural position. 



