CRUCIFERAE 81 



MacLeod in Flanders saw a humble-bee, 2 hover-flies, and one of the Lepi- 

 doptera (Bot. Jaarb. Dodonaea, Ghent, vi, 1894, p. 197.) 



176. N. palustre DC. (Kirchner, 'Flora v. Stuttgart,' p. 287; Knuth, 'Bl. u. 

 ilnsekt. a. d. nordfr. Ins.,' pp. 25, 148.) The bright yellow petals are only as long as 



the sepals, so that the flowers are less conspicuous than those of allied species. 

 There are two nectaries at the sides of the base of each short stamen. The anthers 

 of the four long stamens are at the same level as the stigma, while those of the 

 two short ones curve away from it and are somewhat lower. All six dehisce 

 introrsely. The two short stamens are therefore exclusively concerned with cross- 

 pollination, while the four long ones effect automatic self-pollination if insect- 

 visits fail. 



Visitors. I observed at Fohr one hover-fly (Eristalis sp.) ; while MacLeod 

 in Flanders noticed 3 insects of the kind (Bot. Jaarb. Dodonaea, Ghent, vi, 1894, 

 p. 197). 



In Dumfriesshire (Scott-Elliot, ' Flora of Dumfriesshire,' p. 1 1), Meligethes and 

 2 Muscidae have been recorded. 



177. N. lippiense DC. 



Visitors. Schletterer observed the following Apidae at Pola. 



1. Andrena albopunctata Rossi; 2. A. carbonaria L. ; 3. A. combinata Chr. ; 

 4. A. convexiuscula K.\ 5. A. flavipes Pz. ; 6. A. nana K.\ 7. A. parvula K. ; 

 8. Halictus calceatus Scop. ; 9. H. fasciatellus Schenck; 10. H. levigatus K. 5 ; 11. 

 H. morio F. ; 12. Prosopis clypearis Schenck. 



178. N. pyrenaicum R. Br. (= Roripa pyrenaica Reichb.). (MacLeod, 

 ' Pyreneenbl.') The yellow flowers have a diameter of 5-5 mm. when expanded. 

 There are four nectaries, of which the two situated between the pairs of long stamens 

 are very small. At the end of flowering, automatic self-pollination is effected by 

 contact of anthers and stigma. Nectar-seeking insects which visit the flowers mainly 

 effect cross-pollination. 



Visitors. MacLeod observed in the Pyrenees a short-tongued bee (Halictus), 

 and 2 Muscidae. 



52. Barbarea R. Br. 



Homogamous yellow flowers with half-concealed nectar. There are six nectaries, 

 of which the pair at the base of each short stamen frequently coalesce. 



179. B. vulgaris L. (Herm. Miiller, 'Weit. Beob.,' I, pp. 325-6; Kirchner, 

 'Flora v. Stuttgart/ p. 288; Knuth, ' Bloemenbiol. Bijdragen.') The golden yellow 

 petals spread out in the sun to a diameter of 7-9 mm. At the base of each short 

 stamen is a small fleshy green nectary on either side, the two often being united into 

 a semicircular ridge. There is also a larger elongated tooth-like nectary outside and 

 between the bases of each pair of long stamens, and corresponding to two short 

 stamens which have disappeared. These last produce only a small drop of nectar, 

 while the four other nectaries or the two ridges resulting from their union secrete 

 abundantly in favourable weather. This nectar collects in dilatations at the bases 

 of the two outer sepals, and in such quantity that the stamens to use Miiller's 



