July 15, 1915 Heredity of Color in Phlox Drummondii 301 



Observed and Calculated Ratios 



The observed and calculated ratios are again equal, with the excep- 

 tion of the preponderance of white, which is unaccounted for. 



SUMMARY 



Plant COLORS in Phlox drummondii. — (i) White is due to the absence 

 of pigment and to the reflection of light from the cells. (2) Green color 

 is caused by the presence of a green pigment in the chlorophyll. (3) 

 Yellow, cream, and related colors are due to a yellow pigment either 

 associated with green in the chloroplasts or found alone in the chromo- 

 plasts; generally the latter. Yellow may sometimes come from the cell 

 sap. (4) Red color may under certain circumstances be due to the 

 presence of that pigment in the chromoplasts, but is ordinarily a cell- 

 sap color. (5) Most of the remaining colors, purple, blue, generally red, 

 pink, etc., are due to pigments in the cell sap. (6) Many of the colors 

 and shades found in flowers are the result of both plastid colors and 

 cell-sap colors acting together in various proportions. (7) Certain of 

 the denser plastids or cell-sap colors may cover up the more delicate 

 colors so that they can not be seen. (8) Finally, the color in the cell sap 

 may be due to the relative presence of a non-nitrogenous chemical sub- 

 stance, anthocyanin. This is blue in alkaline and red in an acid-reacting 

 cell sap and, under certain conditions, also dark red, violet, dark blue, 

 and even blackish blue. Anthocyanin can be obtained from the super- 

 saturated cell sap of a number of deeply colored parts of plants in a 

 crystalline or amorphous form. Blood-colored leaves, such as those of 

 the copper beech, owe their characteristic appearance to the united 

 presence of green chlorophyll and anthocyanin. The different colors of 

 flowers are due to the varying color of the cell sap, to the different distri- 

 bution of the cells containing the colored cell sap, and also to the com- 

 binations of dissolved coloring matter with the yellow, orange, and red 

 chromoplasts and the green chloroplasts. There is occasionally found in 

 the cell sap a yellow coloring matter known as " xanthein," nearly related 

 to xanthophyll, but soluble in water. 



Color inheritance in Phlox drummondii. — The following unit char- 

 acters were found in the four varieties of Phlox drummondii that were 

 used in these experiments: (i) A dark eye factor producing a dense 

 coloration at the center of the flower. This was dominant over its 

 absence, the white eye, which was exhibited in more or less of a definite 

 pattern. (2) A blue factor. (3) A red factor. (4) An intensifying 

 factor which determines the degree of pigmentation of the reds. (5) A 

 yellow factor which acts only in the presence of the eye factor. 



The reds and blues are cell-sap colors, and the yellow is due to the 

 presence of yellow chromoplasts. 



Studies of this nature will eventually lead to a time when color and 

 color inheritance are sufficiently understood and controlled to be of great 

 commercial value to the florist or grower of ornamental plants. 



