OBJECTIONS OF THE THEORY 297 



some other plants) the circumferential flowers have their 

 corollas much more developed than those of the centre, 

 and this seems often connected with the abortion of the 

 reproductive organs. It is a more curious fact, previously 

 referred to, that the aclienes or seeds of the circumference 

 and centre sometimes differ greatly in form, color, and 

 other characters. In Carthamus and some other Oom- 

 positae the central achenes alone are furnished with a 

 pappus; and in Hyoseris the same head yields achenes 

 of three different forms. In certain Umbelliferse the 

 exterior seeds, according to Tausch, are orthospermous, 

 and the central one coelospermous, and this is a character 

 which was considered by De Candolle to be in other 

 species of the highest systematic importance. Prof. 

 Braun mentions a Fumariaceous genus, in which the 

 flowers in the lower part of the spike bear oval, ribbed, 

 one-seeded nutlets; and in the upper part of the spike, 

 lanceolate, two-valved, and two-seeded siliques. In these 

 several cases, with the exception of that of the well- 

 developed ray-florets, which are of service in making the 

 flowers conspicuous to insects, natural selection cannot, as 

 far as we can judge, have come into play, or only in a 

 quite subordinate manner. All these modifications follow 

 from the relative position and inter-action of the parts; 

 and it can hardly be doubted that if all the flowers and 

 leaves on the same plant had been subjected to the same 

 external and internal condition as are the flowers and 

 leaves in certain positions, all would have been modified 

 in the same manner. 



In numerous other cases we find modifications of 

 structure, which are considered by botanists to be gener- 

 ally of a highly important nature, affecting only some of 



