174: MORPHOLOGICAL DEVELOPMENT. 



corolla are long and flexible, the radial form is scarcely at 

 all modified. On bearing in mind the probable relations of 

 the forms to insect-agency, the meaning of this difference 

 will not be difficult to understand.* 



236. In extremely-varied ways there are thus re-illus- 

 trated among flowers, the general laws of form which leaves 

 and branches and entire plants disclose to us. Composed as 

 each cluster of flowers is of individuals that are originally 

 similar; and composed as each flower is of homologous foliar 

 organs; we see both that the like flowers become unlike and 

 the like parts of each flower become unlike, where the posi- 

 tions involve unlike incidence of forces. The symmetry 

 remains radial where the conditions are equal all round; 

 shows deviation towards two-sidedness where there is slight 

 two-sidedness of conditions; becomes decidedly bilateral 

 where the conditions are decidedly bilateral; and passes into 

 an unsymmetrical form where the relations to the environ- 

 ment are unsymmetrical. 



* It has been pointed out to me that " the extreme development of the 

 corolla so often found in the outer flowers or on the outer side of the outer 

 flowers in closely packed inflorescences, associated as it often is with disap- 

 pearance of stamens or carpels or both, is usually put down to specialization 

 of these outer flowers for attractive purposes. Since the whole inflorescence 

 is increased in conspicuousness by such a modification, it is supposed that 

 natural selection favoured those plants which sacrificed a portion of their 

 seed-bearing capacity for the supposed greater advantage of securing more 

 insect visits." But granting this interpretation, it may still be held that 

 increase of attractiveness due to increase of area must be achieved by florets 

 at the periphery, and that their ability to achieve it depends on their having 

 an outer, unoccupied, space which the inner florets have not; so that, though 

 in a more indirect way, their different development is determined by different 

 exposure to conditions. 



