THE LABURNUM 23 



tube which they make round the ovary ; but, since in 

 the genus Gytisus and a few allied groups, such as the 

 Furze, all ten stamens are united, this tube is a com- 

 plete one, so that the honey is effectually concealed 

 at some depth within the flower, and only a clever 

 insect with a tolerably long tongue can reach it. The 

 anthers, moreover, ripen their pollen rather before the 

 surface of the stigma shows by its stickiness, that it is 

 ready to receive the pollen-grains ; and just below 

 the stigma is a circle of hairs which may hinder the 

 pollen of the stamens from reaching it. 



All this complex structure is a special adaptation for 

 cross-pollination by bees; and, in striking contradiction 

 to Pliny's statement, bees are the chief insects which 

 visit Laburnum blossoms. Alighting upon the wing- 

 petals, the insects depress them by their weight ; and 

 as the wing-petals are moulded with a protuberance 

 fitting into a corresponding hollow in the keel-petals, 

 the latter are depressed at the same time. This 

 exposes the stamens and stigma until the bee's weight 

 is removed, when they will be again covered by the 

 keel-petals. It would seem that in a freshly-expanded 

 blossom only the short stamens are protruded, and 

 they will dust the abdomen of the bee with pollen ; 

 but when the flower is a day or two older the pistil 

 and longer stamens emerge and deposit pollen on the 

 back of the visiting insect. Thus the pollen obtained 

 at these two siages of development will reach stigmas 

 of other flowers differing in the length and progressive 

 curvature of their styles. To reach the honey the bee 

 bores through a swelling just below the standard 

 petal. Possibly at a later stage, if not already cross- 



