74 ANGIOSPERMAE—DICOTYLEDONES 



IX. ORDER CRUCIFERAE JUSS. 



Literature. — Herm. Miiller, 'Fertilisation,' pp. 100-14; Knuth, ' Bl. u. Insekt. 

 a. d. nordfr. Ins.,' p. 24. 



The Cruciferae are all entomophilous, and most of them are homogamous. 

 By elongation of the floral axis the inflorescence, which is usually an umbel to 

 begin with, becomes a raceme, that renders the plant more or less conspicuous 

 according to the size and number of the flowers. But few species of this order, 

 however, are so conspicuous that insect-visits are very numerous. It follows that 

 almost all Cruciferae are capable of automatic self-pollination. 



The calyx not only protects the developing flower, but in many cases holds 

 the claws of the petal together in such a way that they form a short tube at the 

 bottom of which the nectar lies. Insects are attracted by the petals, which are 

 usually yellow or white, more rarely violet, blue, or red. In spite of marked 

 uniformity in the structure of their flowers, the Cruciferae present so much diversity 

 in the number and position of the nectaries, in the relation of the stamens to these 

 and to the stigma, as well as in the mode of storing and concealing nectar, that 

 hardly any two species completely agree in all these details. 



The number and position of the nectaries have been investigated very thoroughly 

 by J. VelenovskJ''. His researches were made on 170 species, including all the 

 European Cruciferae and a few exotic forms. He gives drawings of the anterior 

 and lateral aspects of the nectaries in 123 species (belonging to fifty -five genera). 

 According to him, no species is devoid of them. When a stamen is reduced, the 

 nectary develops into a rounded swelling. The size of these organs is usually 

 proportionate to the size of the flower, but to this there are exceptions. Heliophila 

 amplexicaulis, for instance, has much smaller flowers than Malcolmia maritima, 

 yet its nectaries are much larger than those of the latter. The largest upper nectaries 

 are found in Crambe maritima : the smallest in Stenophragma thalianum, and 

 Lepidium ruderale. The lower nectaries — i. e. those at the bases of the short 

 stamens — are always present, though in many cases they may be small, or even 

 almost vestigial, as in Crambe maritima and C. cordifolia. The upper nectaries, 

 on the other hand, are very frequently absent, and some species of a genus may 

 possess them, while they are lacking in others. The position of these organs has 

 special relation to the structure and form of the fruits. 



VelenovskJJ groups the Cruciferae with reference to the structure of the nectaries 

 as follows. — 



I. Siliquosae. 



Upper and lower glands always present, usually with distinct lateral ridges. 



1. Cheirantheae. Only the lower nectaries are free anteriorly and posteriorly. 

 (Cheiranthus, Matthiola, IMalcolmia, Hesperis, Chorispora.) 



2. Erysimeae. Upper and lower nectaries either free, or united by a weak 

 lateral ridge : the lower open anteriorly, closed posteriorly, where they are usually 

 thickened. (Barbaraea, Nasturtium, Armoracia, Roripa, Erysimum, Conringia, 

 Alliaria.) 



