428 



HUTCHIXSOX'S POPULAR BOTANY 



L 



Photo by] 



FIG. 531. NEEDLE WHIN (Genista anglica). 



IE. Step. 



One of the Pea-flower tribe. The flowers do not open unless visited by insects, when the insect's weight causes the 

 flower to explode, as it were, and cover it with a shower of pollen. 



flowers. In Chapter X we described the several parts of a flower of the 

 Pea, and showed the adaptation of those parts to its chief pollinators bees. 

 We saw that the stamens and pistil are contained in the keel or carina of 

 the blossom, those two cohering petals which protect the anthers from 

 pollen-feeding insects, and that the alse or wings i.e. the two lateral petals 

 afford a platform for the bee guest, as well as serve as a lever to depress the 

 keel. The last fact is of much importance owing to the effect attending 

 such depression an effect which will be explained in a moment. 



We will suppose that fig. 497 represents a pea-blossom which is about to 

 be visited by a bee. The flower is giving forth its seductive odour: the 

 bright standard is fully spread ; a supply of nectar has flowed into the 

 staminal tube : and the anthers have discharged their moist, sticky pollen 

 into the conical part of the keel, thereby covering the tiny brush with which 

 the end of the unripe style is provided. All is ready. Presently the bee 

 alights : and as its weight falls upon the wings of the flower the keel is 

 depressed. At once the piston mechanism comes into play, for the style, 

 being a fixture, does not yield to the depression, and so the pollen-laden 

 style-brush is thrust through the apical hole of the keel. Here it comes in 

 contact with the breast of the bee, which gets plentifully smeared with the 



