I THK SHAPES OF FLOWEKS. 153 



liable to alter in consequence of altered relations to sun and 

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

 ing modifications : the smaEer 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. n-tg 

 219, 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 

 m.ust 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, wiU 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 



