80 FLOWERS OF THE HEATHS AND MOORS 



The height of a Broom plant is about 6 ft. It is in flower in 

 April, May, and June. The plant is an evergreen shrub, increasing 

 by seed. 



The flowers are, as in Genista, explosive. There is no honey. 

 The 5 short stamens first explode and dust the insect's abdomen, the 5 

 longer stamens then dust it above, and the pollination of the stigmas 

 not covered up ensues. When bees settle they grasp the alse with 

 their mid and hind legs, and thrust their forelegs and head below the 

 middle of the vexillum or standard. 



The alae and carina are forcibly pressed down, and the united upper 

 margin of the keel splits from behind forwards by the pressure of 

 an insect's foot. A fold catching in the angle between the upper edge 

 of the carina and the sharp pouched protuberance at its mouth con- 

 nects the alse with the carina. When the split extends to the middle 

 the shorter stamens spring out. They open in the bud and now press 

 the pollen against the closed upper edge of the carina, and force the 

 pollen against the bee's abdomen. The shock is not sufficient to drive 

 off the bee, which only pauses and resumes its work. The split 

 extends still further, and has barely reached the tip of the style, closely 

 pressed against the keel, when a second more violent explosion takes 

 place. Before this the style lay along the side of the carina, and the 

 flattened end lies in the apex of the carina above the longer anthers, 

 which have already opened. It curls inwards being now rendered free, 

 and forms more than one complete spiral turn. As soon as it extends 

 to the end of the carina the style springs up, and strikes the bee's 

 back with the stigmatic tip, and the bulk of the pollen carried away 

 by the enlarged style falls on the bee's back. The long stamens curl 

 inward and emerge from the flower. When the bee is held, and the 

 stigma cannot slip sideways, it remains as if stunned, and then, turning 

 round, forces itself away from the style, and begins to gather pollen 

 from the anthers. When the vexillum is erect, and the alse are still 

 enclosed by it, humble bees force it open and cross-fertilize it. The 

 visitors are Hymenoptera (Apidse), Diptera (Syrphidse), Coleoptera 

 (Staphylinida,-, Niticlulidse). 



Broom is dispersed by its own agency. The fruit is a dry pod, 

 which jerks its seeds by an elastic movement, to a distance, opening 

 suddenly with a jerk. It is also myrmecochorous, or dispersed by 

 ants, which find nutriment in the elaiosomes. 



Broom is a heath plant requiring a sand soil, and is thus a sand- 

 lover, but some degree of humus soil is also a necessity, and it is like- 

 wise partly a humus-lover. 



