CRUCIFERAE 121 



91. Aethionema R. Br. 



300. A. saxatile R. Br. — According to Briquet (' ]£tudes d. biol. flor. d. les 

 Alpes Occident.') the upright sepals are edged with white, while the red-veined white 

 or bright rose-red petals spread out above. The stigma is at first beneath the 

 anthers, but subsequently the style elongates. Kirchner adds that the flowers are 

 slightly protogynous, that the diameter of the upper part of the corolla is 3-4 mm., 

 and that automatic self-pollination is regularly effected by the anthers of the four 

 long stamens. 



Visitors. — These are flies and small beetles, which chiefly effect self- but 

 occasionally cross-pollination. 



301. A. grandiflonun Boiss. et Hohen. — Hildebrand says that this species is 

 self-sterile (Ber. D. bot. Ges., Berlin, xiv, 1896, p. 324). 



92. Coronopus Haller. 



Small, white, homogamous to protogynous flowers, with half-concealed nectar. 

 Four nectaries. 



302. C. Ruellii All. (Kirchner, ' Flora v. Stuttgart,' p. 312; MacLeod, Bot. 

 Jaarb. Dodonaea, Ghent, vi, 1894, p. 213 ; Knuth, ' Weit. Beob. ii. Bl. u. Insekt. a. d. 

 nordfr. Ins.,' ' Bl. u. Insekt. a. Helgoland ' ; Warnstorf, Verh. bot. Ver., Berlin, xxxviii, 

 1896.) — The small white flowers are arranged in dense helicoid inflorescences in 

 the forks of the branches, especially in the middle of the plant, which is closely 

 applied to the ground. The diameter of the flower is only 4 mm. On either side 

 each short stamen — and therefore apposed to a petal — there is a relatively large 

 green nectary, which secretes so abundantly that the base of the ovary glistens 

 all round. When the flower opens all the anthers are still unripe, and at the same 

 level as the stigma, which would appear to be already mature. When the petals 

 expand the stamens curve away from the stigma, on the side facing which they 

 dehisce almost simultaneously. Cross-pollination may therefore result from insect- 

 visits. Failing these, however, automatic self-pollination is ensured later on, by 

 the petals inclining together and bringing the anthers into direct contact with the 

 stigma. Warnstorf says that two of the sepals bend inwards during anthesis, pressing 

 the long stamens against the stigma so that autogamy takes place. The pollen- 

 grains are whitish, ellipsoidal, closely tuberculated, 25-30 /x, long and 15-18 fx. 

 broad. 



Visitors. — In Helgoland I observed 2 small Muscidae, i. e. Coelopa frigida Fall. 

 and Fucellia fucorum Fall, both skg. 



93. Isatis L. 



Small, yellow, homogamous flowers, with half-concealed nectar. Six nectaries. 



303. I. tinctoria L. (Kirchner, ' Flora v. Stuttgart,' p. 313; Knuth, ' Bloemen- 

 biol. Bijdragen.') — In spite of the smallness of the individual flowers the inflorescences 

 are very conspicuous owing to their size. Kirchner says that the six nectaries are 

 situated between the six stamens, which curve outwards so as to be a long way 



