ON THE WATSONIA 



ones in existence before there were flowers of 

 pure violet or of deep red. 



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 

 pigments 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 development of 

 red flowers or of violet ones. In other cases white- 

 ness 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 pre-supposes the modifica- 

 tion 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 



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