CRUCIFERAE 125 



99. Crambe Tourn. 



Moderately large, white, slightly protogynous flowers, with half-concealed 

 nectar. Four nectaries. 



310. C. maritima L. (Knuth, Bot. Centralbl., Cassel, xliv, 1890, pp. 305-8.) — 

 The flowers — of which the diameter is 12 mm. — possess an odour of honey, and 

 are aggregated into large crowded inflorescences. The reddish-white sepals project 

 outwards and upwards, supporting the expanded petals, the white limbs of which 

 are almost horizontal. The claws of the petals are at first yellowish- green, sub- 

 sequently becoming bright violet-red. The filaments and style pass through the 

 same changes of colour, but the anthers and stigma are yellow throughout anthesis. 

 The interior of a young mature flower is therefore yellowish-green, while that of 

 an older one is of a discoloured violet. At the base of each pair of long stamens 

 there is a large rounded green nectary, to which the drop of nectar remains clinging. 

 On the inner side of each short curved stamen there is also a much smaller nectary 

 of the same colour. The filaments of the long stamens are forked, and their anthers 

 are borne on the branches adjacent to the short stamens. Owing to the forking 

 of the filaments the heads of nectar-seeking insects have to be thrust into the flower 

 at defined spots, contact with anthers and stigma being thus secured. 



The stigma matures in the bud— while the anthers are still unripe — and at 

 the beginning of anthesis is situated in the entrance of the flower. The filaments 

 elongate very soon after, thus bringing up the anthers from beneath the stigma. 

 Dehiscence then takes place. The anthers of the long stamens are now somewhat 

 higher than the stigma, while those of the short ones are at the same level. 



Visitors. — Insects while probing for nectar — provided they are large enough to 

 touch anthers and stigma simultaneously — will regularly effect crossing if they thrust 

 their heads into the flower only once. The honey-bee behaved in this way. Other 

 insects of about the same size, e. g. some of the hover-flies (Eristalis tenax L., 

 Syrphus ribesii Z.) did not always do so, and therefore sometimes effected self- 

 pollination. Another hover-fly (Syritta pipiens L.) when sucking nectar was too 

 slender to touch both stamens and carpels, being therefore of no use to the plant. 

 The same is true for two Muscidae (Borborus sp., and Phora pulicaria Fall). I also 

 found in the flowers numerous small po-dvg. beetles (Meligethes brassicae Scop., 

 more rarely M. viridescens F), as well as their larvae. The adults in most cases 

 effect self-pollination, but may also occasionally bring about cross-pollination. The 

 larvae of Meligethes are found not only in the fully developed flowers, but also 

 in the buds, where they are very abundant. They destroy the stamens and pistil, 

 so that many flowers are infertile. The question arises whether the beetles and 

 their larvae are to be regarded only as enemies of the plant. I am inclined to 

 maintain the negative, for these small insects are apparently among the most 

 important, if indeed they are not the chief pollinators of the species; and if they 

 and their larvae are present in but small numbers, many flowers would remain 

 unfertiUzed, though it is true that many others would escape destruction. On 

 the other hand, should the beetles be too numerous the damage outweighs the 

 benefit. The beetles, however, will then suff'er proportionately, for only a small 

 number will be able to develop, and this again will react unfavourably upon pollination. 



