246 GENETICS 



tain conditions changes the colors, as does alteration of the 

 genes. Some of the relations are the following: 



D. The "sun-red" type requires exposure to the sun for 

 production of the red color. Parts protected from the sun 

 are green. In the "green" types, on the other hand, subjec- 

 tion to the sun does not cause the production of red color. 

 Thus the difference between red and green plants is due 

 in some cases to diversity of genes, as when "sun-red" and 

 "green" types are both grown in the sun. In other cases 

 the difference between red and green plants is due to en- 

 vironmental difference, as when "sun-red" plants grown in 

 the sun are compared with those of the same type grown 

 in the shade. 



The plants of the "purple" type do not depend on ex- 

 posure to the sun for their color; they are purplish in color 

 whether grown in sun or shade. 



The degree of color produced by exposure to the sun 

 depends on what genes are present. In the typical "sun-red" 

 variety, exposure to the sun causes a red color widely dis- 

 tributed on the plant. In the "dilute sun-red," exposure to 

 the sun under similar conditions causes only a little red, at 

 the bottom and tips of the leaves, while in the "green" 

 type, no red appears. 



E. The nature of the soil affects the color. "Dilute sun- 

 red" grown in poor soil and subjected to the sun has almost 

 all parts red; in good soil with the same relation to the 

 sun, it has very little red. The "green" and "brown" types 

 are not influenced in their color by the nature of the soil. 



F. Certain particular chemicals In the soil affect the 

 color. Presence of much nitrogenous matter tends to sup- 

 press the red; If httle Is present the red color is marked. 



G. Storage of carbohydrates in the leaves of the color- 

 producing varieties causes increase of the red color. The 

 amount of carbohydrate in the leaves may be Increased by 

 experimental procedures, as by removing the growing ears. 



