30 NATURE SKETCHES IN TEMPERATE AMERICA 



such as the wild columbine, eject their small seeds by the burst- 

 ing open of their capsules. 



Wallace intimates a suggestive fact that dominant groups 

 of our large forest trees, such as oaks and beeches, are among the 

 most ancient of known dicotyledonous plants, going back to 

 the cretaceous period with little change of type, so that it 

 is not improbable that they may be older than any fruit-eating 

 mammal adapted to feed upon their fruits. The attractive 

 colored fruits, according to Grant Allen, on the other hand, 

 having so many special adaptations to dispersal by birds and 

 manmials, are probably of more recent origin. 



Wallace maintains, "The apple and the plum tribes are 

 not known earlier than the miocene period; and although the 

 record of extinct vegetable life is extremely imperfect, and the 

 real antitjuity of these groups is no doubt very much greater, 

 it is not improbable that the comparative antiquity of the 

 fruit-bearing and nut-bearing trees may remain unchanged 

 by further discoveries, as has almost always hapi)ened as 

 regards the comparative antiquity of animal groups." 



At the present time adaptation "is precisely one of the 

 things evolutionists are trying to find the causes or causal 

 factors of. But nevertheless the adaptability of life stuflF, 

 its plasticity and capacity of advantageous reaction, is, 

 to many biologists, a fundamental fact in organic nature, 

 like gravitation or chemical affinity in organic nature; a thing 

 basic and inexj)lirable, and in itself a factor whose consequences 

 are to be determined but not further to be questioned as to 

 their cause." ' 



Flower and Insect Adaptations 



Lubbock says that "not only have the form and colors, 

 the bright tints, the sweet odors, and the nectar been gradually 

 developed by the force of an unconscious selection exercised 

 by insects, but even the arrangement of colors, the shape, the 

 size, and the position of the petals, the relative position of the 

 stamens and pistil are all determined by the visits of the insects, 

 and in such a way as to assure the great object (fertilization) 

 that these visits are intended to effect." 



' Jordan and Kellogg, " Evolution and Animal Life," p. 56. 



