CRUCIFERAE 103 



Beitrage,' II, p. 15; Herm. Miiller, ' Alpenblumen,' p. 150.) Only the two smaller 

 of the four nectaries are functional. These are situated on the inner side of the 

 bases of the two short stamens. The two others are much larger, are placed 

 external to the bases of the pairs of long stamens, and face obliquely outwards. 

 The two sepals opposite the functional nectaries are erect, while the two others 

 are horizontal. The short stamens turn the dehisced sides of their anthers inwards ; 

 the anthers of the long stamens are directed towards the short ones. Insects 

 probing for nectar must therefore usually effect cross-pollination. Failing insect- 

 visits self-pollination results from contact between the anthers and stigma. 



Visitors. Hermann Miiller observed 2 Muscidae, 2 Apidae (Halictus), and a 

 Lepidopterid in the Alps. Schulz noticed numerous flies and Lepidoptera, more 

 rarely Hymenoptera and beetles. MacLeod in Flanders saw 2 hover-flies, and a 

 Lepidopterid (Bot. Jaarb. Dodonaea, Ghent, vi, 1894, p. 202). 



239. D. muralis DC. (Kirchner, 'Beitrage,' pp. 23-4.) The flower mechanism 

 essentially agrees with that of the last species, but all four nectaries are functional, 

 and the four sepals all oblique. The flowers have a diameter of 16-20 mm. The 

 limbs of the petals are so broad that they somewhat overlap. When the flower 

 opens the anthers are ripe, and the stigma fully mature. The latter is at first either 

 rather lower than the anthers of the four long stamens, or just at the same level. 

 These anthers turn their dehisced sides outwards, but automatic self-pollination 

 is inevitable, for they are coated almost all round with pollen, and quite near the 

 stigma. When the flowers have completely opened the stigma projects beyond 

 the anthers of the long stamens, so that cross-pollination is favoured when insects 

 visit the flowers. The anthers of the two short stamens are turned inwards, and 

 situated about 3 mm. below those of the long ones. 



Visitors. MacLeod observed the following in Flanders. Apis, a species of 

 Halictus, 4 hover-flies, a Muscid, and a Lepidopterid (Bot. Jaarb. Dodonaea, Ghent, 

 vi, 1894, p. 203). 



69. Eruca DC. 



Large yellowish homogamous flowers, with half-concealed nectar. Four nectaries. 



240. E. sativa Lam. (Hildebrand, ' Vergleich. Untersuchungen ii. d. Saftdr. d. 

 Cruciferen'; Kirchner, 'Beitrage/ p. 21.) The delicate whitish-yellow petals with 

 their dark-brown veins spread out into a cross about 25 mm. in diameter. The 

 flowers are homogamous. The anthers dehisce introrsely, and are placed so close to 

 the stigma that automatic self-pollination is inevitable. Of the four nectaries only the 

 two large flat ones at the inner sides of the short stamens are functional, while the two 

 others situated outside the bases of the two pairs of long stamens do not secrete. 



70. Vesicaria Lam. 

 Yellow flowers, with half-concealed nectar. 



241. V. arctica R. Br. Warming observed in Greenland that fruits were set 

 even at a height of 700 m. Nothing is known about the flower mechanism. 



242. V. utriculata L. Briquet ('Eludes d. biol. flor. d. les Alpes Occident.') 

 gives the diameter of the yellow corolla as 15 mm., and states that the claws of 



