430 XXXI. THE FRUIT. DEVELOPMENT OF THE FLOWER. 



examination of the fully-formed flower must precede any attempt 

 to study its development. The inflorescence of the rape is a 

 raceme, of which the apex continues to develop for some time, so 

 that the young flowers are crowded together as into a corymb. 

 The flowers are stalked, ebracteate. They bear four linear, 

 greenish sepals, in two pairs, of which the outer are, so far as 

 relations with the axis of the inflorescence are concerned, in 

 the middle plane, that is, are antero-posterior, and the inner pair 

 are at right angles to them, and are therefore lateral. In the bud 

 the inner have their edges very recognisably covered by the outer 

 sepals, and their respective positions are easy to determine (Fig. 

 152). Four petals follow the four sepals, and alternate with 

 them as if the latter also formed one whorl of four. The petals 

 are obovate, and stalked, so that we can distinguish limb and 

 claw, After these four diagonally placed petals, come two laterally 

 situated short stamens, to which follow, in the middle plane, two 

 pairs of longer stamens. Finally comes the 

 narrow, laterally-compressed pistil, gradually 

 tapering into the style, and with a feebly two- 

 armed stigma. 



Cross-sections through the ovary show that 

 ** * S kilocular ; but in order to cut through the 

 insertion of one of the (usually six) ovules it 



is necessary to cut through the lower third of 

 FIG. 152. Diagram of ,1 mi J.-.L- 1-1 T -i ^i 



a Cruciferous flower. ^ ne ovary. The partition which divides the 



ovarian cavity in the median plane is a false 

 one, known as the replum, and the placentation is parietal, on 

 the angles which this partition makes with the wall of the 

 ovary. The pistil consists, therefore, of two laterally-placed 

 carpels, which coalesce only by their edges, so that the placentae 

 would naturally have been in contiguous pairs upon an unilocular 

 ovary, had the replum not been present to separate the carpels, and 

 placentae appertaining to them, from one another. 



In order to work out the development we take the tip of a 

 young inflorescence, and first remove from it all the larger flower- 

 buds, up to those the height of which does not exceed ^V inch. 

 We then continue the process under the dissecting microscope, 

 using no water to the object, until only the innermost flower 

 rudiments remain. Close beneath these we cut the axis of the 

 inflorescence across, so that they are left standing erect. We can 

 now add a drop of water, cover with a cover-glass, and remove 



