THE FLOWER. 61 



A bee visiting the different flowers would brush some 

 part of the body against the anthers of the long stamens, 

 and another part agaiust the anthers of the short stamens ; 

 and these same parts (which, of course, would have pollen 

 adhering to them) coming in contact with long and short 

 pistils respectively, the pollen of one flower would in each 

 case be applied to a stigma of another flower ; or, in other 

 words, cross-fertilization would necessarily result. It is 

 found, besides, that the 

 pollen grains of the 

 two sets of stamens 

 are of different size, 

 and each less active 

 upon its own stigma 

 than upon the stigma 

 of another flower. In 

 some genera three sets 

 of flowers with sta- 

 mens and pistils of differing lengths exist (trimorphism), 

 evidently designed for intercrossing. 



78. There are other adaptations for cross-fertilization 

 besides dichogamy and dimorphism. An interesting case 

 is fuimshedhj papilionaceous flowers ; for example, the Pea 

 (Figs. 141-143). The ten stamens and single pistil are 

 enclosed within the keel (Fig. 141). There are hairs on 

 the style below the stigma, and these loosely retain the 

 pollen which is discharged early by the anthers, the latter 

 remaining in the keel. When a bee alights on the wings 

 (Fig. 142, a) and keel (Fig. 142, k) they are together 



Figs. 139, 140. Dimorphic flowers of Houstonia : 139. Pistil short ; 140. Pistil 

 long. 



