168 MORPHOLOGICAL DEVELOPMENT. 



not absent; and a shape otherwise determined is hence less 

 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- 

 ** 9 KH^ ganic world are here quite inoperative. Fig. 



249, representing a species of Campanula, 

 shows that the developments of individual 

 flowers are somewhat modified by the rela- 

 tions of their parts to general conditions. But 

 the fact to be observed is, that the extreme 

 transformations 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 these functions, under conditions that are 

 extremely varied, an adequate cause for the different types 

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

 are parts in which fertilization is effected; and the active 

 agents of this fertilization are insects — bees, moths, butter- 

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

 forms and positions of the essential organs of fructification, 

 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 their 

 shapes to flowers, similarly arise by the survival of indi- 

 viduals which have the subsidiary parts so adjusted as to aid 

 this fertilizing process — the deviations from radial symmetry 

 being among such adjustments. The reasoning is as fol- 

 lows. 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 



