CRUCIFERAE 91 



*ong stamens which face inwards are in the throat of the corolla, and the 



simultaneously maturing stigma is 1-2 mm. beneath them. The stigma expands 

 to right and left, and is longitudinally cleft into two lobes, the narrow ends of 

 which are reflexed. The two short stamens also direct their pollen-covered surfaces 

 towards the middle of the flower, and are so close to the stigma that their tips 

 are at the same level as, and about 1 mm. distant from its reflexed lobes. The 

 lone or two narrow nectar-passages run between the end of the pistil and the short 

 $ stamens, so that the proboscis of a moth probing for nectar must touch the stigma 

 Iwith one side, and the pollen of a short stamen with the other. After the proboscis 



has been dusted with pollen all round cross-pollination must be effected in every 

 new flower visited. Should insect-visits fail the stigma pushes up between the four 

 J long stamens and dusts itself with pollen, effecting automatic self-pollination which 

 1 according to Hermann Miiller' s experiments is effective, though Hildebrand asserts 



(Ber. D.bot. Ges., Berlin, xiv, 1896) that the species is self-sterile. In the early stage 

 i of anthesis the only use of the long stamens is to keep unbidden guests from the 



nectar by blocking the entrance of the flower with their anthers. 



Visitors. Agnes Miiller daughter of Hermann Miiller observed the following 

 1 during a few mild evenings in May. Three Noctuidae : 1. Dianthoecia nana Hufn. ; 

 i 2. Hadena sp. ; 3. Plusia gamma Z., freq. : also the Geometrid Iodis lactearia Z., 

 'and the Pyralid Pionea forficalis Z. In these moths the proboscis is from 11- 

 ; 18 mm. long. 



58. Malcolmia R. Br. 



Flowers of considerable size, with concealed nectar. 



211. M. maritima R. Br. Kerner says that in this species there are two rows 

 of erect stiff-pointed bristles on the ovary, to prevent any insect from probing for 

 nectar, except in such a way that its proboscis and head touch the pollen-covered 

 anthers and the stigma. The plant is self-fertile according to Hildebrand (Ber. D. 

 bot. Ges., Berlin, 1896). 



59. Sisymbrium L. 



Small yellowish or whitish flowers, homogamous to slightly protogynous, with 

 half-concealed nectar. Nectaries two, four, or six. 



212. S. officinale Scop. (Herm. Miiller, 'Fertilisation,' pp. 109-10, 'Weit. 

 Beob.,' II, p. 202 ; Knuth, ' Bl. u. Insekt. a. d. nordfr. Ins.,' p. 26.) The small bright 

 yellow flowers are only 3 mm. in diameter. There is a nectary on either side the 

 base of each short stamen, and the nectar secreted collects on each side in the angle 

 bounded by a short stamen, a long stamen and the pistil. The dehisced surfaces 

 of the anthers of the long stamens are at first on the same level as, and almost 

 touching, the stigma, both they and it projecting a little from the flower. The 

 two short stamens are meanwhile still concealed within the corolla, but their anthers 

 have also dehisced. All the stamens now grow a little, the long ones stretching 

 beyond the stigma, and inclining together above it, while the short ones which 

 are now as long as the pistil diverge outwards to some extent. 



An insect visitor may therefore effect either cross- or self-pollination. As insect- 

 visits are few, automatic self-pollination frequently takes place by pollen falling on 



