234 



ANGIOSPERMAE—DICOTYLEDONES 



2190. U. vulgaris L. (Buchenau, Bot. Ztg., Leipzig, xxiii, 1865, pp. 93 et 

 seq. ; Hildebrand, op. cit., xxvii, 1869, pp. 505-7; Heinsius, Bot. Jaarb. Dodonaea, 

 Ghent, iv, 1892, pp. 78-9; MacLeod, op. cit., v, 1893, pp. 359-60; Kirchner, 

 'Flora V. Stuttgart,' pp. 640-1 ; Kerner, 'Nat. Hist. PI.,' Eng. Ed. i, II, p. 356.)— 

 In this species the corolla is of a yolk-yellow colour, and orange-yellow streaks on 

 the palate serve as nectar-guides. The lower lip bears the large, thick spur, which 

 is at an angle of 75° to its long axis. On being visited by an insect, the lower lip is 

 so far depressed that the spur points vertically downwards. A bee probing for the 

 nectar secreted by and concealed in the spur brings its head and back into contact 

 with the stigma and the two anthers lying just under the upper lip. The latter are 

 borne on broad, curved filaments, and lie close together. The ovary is situated 

 just behind them, touching the inner surface of the upper lip, the style projecting 

 beyond the stamens, so that an insect visitor touches the stigma first, and, if it brings 



Fig. 322. Z7/rzV:a/<2rz£Z z/«/^arij,Z. (after Hildebrand). (l) Flower, seen from the side: the dotted 

 outline indicates the position assumed by the spur when the lower lip is pressed down (natural size). 

 (2) Stamens and pistil shortly before the flower opens, seen from below. (3) Do., seen from the 



side. (4) Do., seen from above. (5) Do., from a just opened flower, seen from the side : the 



lower stigmatic lobe has bent down. (6) Do. (without the stamens), seen from below, (7) Do., seen 



from above. (S)-(io) The pistil, from the side, above, and below, showing how the lower stigmatic 



lobe, when not hampered by the corolla, bends round strongly upwards after being stimulated. 



pollen from another flower, pollinates it. The stigma consists of two lobes, a short, 

 tooth-like upper one, resting against the upper lip, and a long tongue-shaped lower 

 one, covered with stigmatic papillae on its upper surface. 



As soon as the flower has opened, the anthers dehisce, and the tongue-shaped 

 lobe of the stigma bends downwards, exposing its papillated surface to visitors, which 

 dust it with pollen. The contact serves as a stimulus, causing the lobe to fold 

 upwards and backwards so far that the stigmatic surface is concealed. This prevents 

 autogamy as the insect backs out of the flower. Automatic self-pollination is excluded 

 or is ineff'ective, for the flowers seldom form seeds. Kerner states that if insect-visits 

 fail, the edge of the stigma comes into contact with the anthers and autogamy is thus 

 effected. 



