206 THE OBIOIN OF SPECIES 



flowers. It might have been thought that the develop- 

 ment of the ray-petals by drawing nourishment from the 

 reproductive organs causes their abortion; but this can 

 hardly be the sole cause, for in some Compositse the 

 seeds of the outer and inner florets dilfer, without any 

 difference in the corolla. Possibly these several differ- 

 ences may be connected with the different flow of nutri- 

 ment toward the central and external flowers: we know, 

 at least, that with irregular flowers those nearest to the 

 axis are most subject to peloria, that is, to become abnor- 

 mally symmetrical. I may add, as an instance of this 

 fact, and as a striking case of correlation, that in many 

 pelargoniums the two upper petals in the central flower 

 of the truss often lose their patches of darker color; and 

 when jhis occurs, the adherent nectary is quite aborted; 

 the central flower thus becoming peloric or regular. 

 When the color is absent from only one of the two 

 upper petals, the nectary is not quite aborted but is 

 much shortened. 



With respect to the development of the corolla, 

 Sprengel's idea that the ray-florets serve to attract in- 

 sects, whose agency is highly advantageous or necessary 

 for the fertilization of these plants, is highly probable; 

 and if so, natural selection may have come into play. 

 But with respect to the seeds, it seems impossible that 

 their differences in shape, which are not always correlated 

 with any difference in the corolla, can be in any way 

 beneficial: yet in the Umbelliferse these differences are 

 of such apparent importance — the seeds being sometimes 

 orthospermous in the exterior flowers and coelosperm- 

 ous in the central flowers — that the elder De Candolle 

 founded his main divisions in the order on such char- 



