Retrograde Varieties 149 



cial spots or lines or tracings are to be seen on a 

 white or on a colored background. That such 

 spots and lines are separate units is obvious 

 and is demonstrated by the fact that some- 

 times spotless varieties occur, which in all other 

 respects have kept the colors of the species. 

 The complexity of the color is equally evident, 

 whenever it is built up of constituents of the 

 anthocyan and of the yellow group. The an- 

 thocyan dye is limited to the sap-cavity of the 

 cells, while the yellow and pure orange colors 

 are fixed in special organs of the protoplasm. 

 The observation under the microscope shows at 

 once the different units, which though lying in 

 the same cell and in almost immediate vicinity 

 of each other are always wholly separated from 

 one another by the wall of the vacuole or sap- 

 filled cell-cavity. 



The combination of red and yellow gives a 

 brown tinge, as in the cultivated wall-flower, or 

 those bright hues of a dark orange-red, which 

 are so much sought in tulips. By putting such 

 flowers for a short time in boiling water, the 

 cells die and release the red pigment, which be- 

 comes diffused in the surrounding fluids and the 

 petals are left behind with their yellow tinge. 

 In this way it is easy to separate the constitu- 

 ents, and demonstrate the compound nature of 

 the original colors. 



