ibZ MORPHOLOGICAL DEVELOrMENT. 



that the derivation of a bilateral t}^3e frora it, occurred along 

 with the assumption of an inclined attitude. 



"We come now to a group of cases above referred to, in 

 which radial spnmetry continues to co-exist with that con- 

 stant lateral attitude ordinarily accompanied by the two-sided 

 form. Two examples will suffice : one a very large flower, 

 the Hollyhock, and the other a very small flower, the Agri- 

 mony. Why does the radial form here remain unchanged ? 

 and how does its continuance consist with the alleged general 

 law? 



Until quite recently I have been unable to find any pro- 

 bable answers to these questions. "\Yhen the difficulty first 

 presented itself, I could think of no other possible cause for 

 the anomaly, than that the parts of the Holh^hock- flower, 

 unfolding spirally as they do, might have difierent degrees of 

 spiral twist in different flowers, and might thus not be unfolded 

 in sufficiently-constant positions. But this seemed a very 

 questionable interpretation ; and one which did not obviously 

 apply to the case of the Agrimony. It was only on inquiring 

 what are the special causes of modifications in the forms of 

 flowers, that a more feasible explanation suggested itself ; and 

 this would probably never have suggested itself, had not Mr 

 Darwin's investigations into the fertilization of Orchids led 

 me to take into account an unnoticed agency. 



The actions which affect the forms of leaves, affect much 

 less decidedly the fonns of flowers ; and the forms of flowers 

 are influenced by actions that do not influence the forms of 

 leaves. Partly through the direct action of incident forces 

 and partly through the indirect action of natural selection, 

 leaves get their parts distributed in ways that most facilitate 

 their assimilative functions, under the circumstances in which 

 they are placed ; and their several types of symmetry are thus 

 explicable. But in flowers, the petals and fructifying organs 

 of which do not contain chlorophjdl, the tendency to grow 

 most where the supply of light is greatest, is less decided, if 

 not absent ; and a sliape otherwise determined is hence less 



