THE WATSONIA 87 



In other words, we may feel that the violet- 

 colored flower and the red flower are the 

 newest things in the way of color in the plant 

 world. 



The time of development of white flowers is 

 more debatable. There is reason to suppose that 

 the white flower owes its whiteness to a combina- 

 tion of the conditions which by themselves would 

 be interpreted as greenish yellow and as blue 

 respectively. It is known that these are the only 

 colors that can be compounded to produce the 

 color white. So it is perhaps the safest assump- 

 tion that white flowers were evolved by the 

 hybridizing of greenish yellow ones and blue 

 ones, and that their origin antedates the develop- 

 ment of red flowers or of violet ones. In other 

 cases whiteness is due to air in the cells, and may 

 have been a very recent development. 



Nor is all this a matter of mere unsupported 

 assumption. The inference that such was the 

 sequence of evolution of the different colors 

 seems logical, inasmuch as it presupposes the 

 modification of molecular structure of the flower 

 substance in such a way as to reflect successive 

 rays of light in a graded series or rather in two 

 graded series, one involving shorter and shorter 

 rays as in the flowers that develop from blue to 

 violet; the other involving longer and longer 



