THE SHAPES OF FLOWERS. 153 



liable to alter in consequence of altered relations to sun and 

 air. Gravity, too, must be comparatively ineffective in caus 

 ing modifications : the smaller sizes of the parts, as well as 

 their modes of attachment, giving them greater relative 

 rigidity. Not, indeed, that these incident forces of the inor 

 ganic world are here quite inoperative. Fig. -449 

 2-19, representing a species of Campanula, 

 shows that the developments of individual flow 

 ers are somewhat modified by the relations of 

 their parts to general conditions. But the 

 fact to be observed is, that the extreme trans 

 formations which flowers undergo are not 

 likely to be thus caused : some further cause 

 must be sought. And if we bear in mind 

 the functions of flowers, we shall find in their 

 adaptations to their functions, under conditions that are 

 extremely varied, an adequate cause for the different types 

 of symmetry, as well as for the exceptions to them. Flow 

 ers are parts in which fertilization is effected; and the 

 active agents of this fertilization are insects bees, moths, 

 butterflies, &c. Mr Darwin has shown in many cases, that 

 the forms and positions of the essential organs of fructifica 

 tion, are such as to facilitate the actions of insects in trans 

 ferring pollen from the anthers of one flower to the pistil of 

 another an arrangement produced by natural selection. 

 And here we shall find reason for concluding, that the forms 

 and positions of those subsidiary parts which give the gene 

 ral shape to the flower, similarly arise by the survival of 

 individuals which have the subsidiary parts so adjusted as to 

 aid this fertilizing process the deviations from radial sym 

 metry being among such adjustments. The reasoning is as 

 follows. So long as the axis of a flower is vertical and 



the conditions are similar all round, a bee or butterfly alight 

 ing on it, will be as likely to come from one side as from 

 another ; and hence, hindrance rather than facilitation would 

 result if the several sides of the flower did not afford it equally 



