76 BRITISH FLOWERING PLANTS chap. 



protected by the upper petal. Some- species have a 

 more or less rudimentary pouch at the base of the 

 lower petal, and a corresponding trace of a nectary at 

 the base of the lower group of stamens. This seems 

 to indicate that the one-spurred genera, Corydalis and 

 Fumaria, are descended from two-spurred forms such 

 as Dielytra. 



The flowers of C. cava, according to Hildebrand, are 

 absolutely sterile with their own pollen. The seeds are 

 black and shining, and very finely pitted. 



CEUCIFEE^ 



This great and important order is distinguished by 

 having 4 sepals, 4 petals, and 6 stamens, 4 longer than 

 the remaining 2. The 4 petals are arranged in a cross, 

 whence the name Cruciferse, or cross-bearers. There are 

 2 carpels, united to form, when ripened, a pod. There 

 are at least 1200 species, mostly inhabiting the temperate 

 regions of the old world, but forming a considerable part 

 of the vegetation of Arctic regions. They are almost all 

 insect flowers and homogamous. They present great 



Fia. 45. — Sections of seed ot Hesperis matroncdis, x 10. R, radicle ; C, cotyledons. 

 The radicle is incumbent or parallel with the faces of the cotyledons. 



diff"erences in the number and position of the nectaries, 

 and in the position of these in relation to the stamens 

 and the pistil. The great majority, if not all, produce 

 honey. The seeds are oblong, sub-globose, or flattened 

 and margined or winged, and almost always exal- 

 buminous,^ the embryo occupying the whole seed. The 

 embryo is generally curved, with the radicle incumbent 



' Except in some species of Isatis. 



