THEORIES OF DEVELOPMENT 



ers may be due to a blending of pigments say a 

 mixture of yellow and blue. White may also be 

 due to a prismatic effect induced by the presence 

 of air spaces between the cells. 



It is fairly .clear that different colors may be 

 advantageous for the flower according to the 

 mode of growth of the plant on which the flower 

 is borne. Thus plants that grow in the shadow 

 and those that bloom in the evening advan- 

 tageously bear white or pale yellow flowers, as 

 these are more conspicuous than the most gaudily 

 hued flower would be under the circumstances. 

 On the other hand, a plant that grows in the open 

 may bear a red flower both because that color will 

 be attractive to insects that fertilize the flower 

 and because the reflection of the long waves of 

 light (giving our eye the impression of red) serves 

 to shield the petals from excessive heat. 



If, then, most flowers have the potentialities of 

 wide color variation, there is opportunity for the 

 play of natural selection in adapting each flower 

 to the environment in which the plant on which it 

 grows flourishes to best advantage. 



This theory of flower coloration finds a measure 

 of support in another theory which attempts to 

 explain the peculiar phenomena of " dominance ' ' 

 and "recessiveness" as manifested in Mendelian 

 heredity. According to this explanation, where 

 two antagonistic characters thus Mendelize, the 

 one that is dominant is the newer character and 

 the one that is recessive is the older. This pre- 

 cisely reverses the view that has been suggested 



[37] 



