CHAPTER XV 



ORIGIN AND STRUCTURE OF FLORAL ORGANS ; POLLINATION 



AND FERTILIZATION 



170. The flower a shortened and greatly modified branch. 



In Chapter ix the leaf bud was explained as being an unde- 

 veloped branch, which in its growth would develop into a real 

 branch (or a prolongation of the main stem). Now, since flower 

 buds appear regularly either in the axils of leaves or as terminal 



FIG. 149. Transition from bracts to sepals in a cactus flower 



buds, there is reason to regard them as of a nature similar to 

 leaf buds. This would imply that the receptacle corresponds to 

 the axis of the buds shown in Fig. 85, and that at least some 

 of the parts of the flower correspond to leaves. There is plenty 

 of evidence that this is really true. Sepals frequently look very 

 much like leaves, and in many cactuses the bracts about the 

 flower are so sepal-like that it is impossible to tell where the 

 bracts end and the sepals begin (Fig. 149). The same thing is 

 true of sepals and petals in such flowers as the white water lily. 

 In this flower there is also a remarkable series, ranging all the 



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