50 



chlorophyl l)y oxidation or otherwise. The red eoU)ring 

 uiiitter has been named erythrophyl. 



There are at least two kinds of white color, one a })ignient 

 named leucophyl, the other caused by the absence of all 

 color and generally referred to as chlorotic ; this kind of 

 white is only an o])tical effect of structure, but the two 

 kinds grade into each other without perceptible dividing line. 



Different })igments, as those fixed in the plastids, and 

 others free in the cell sap, often exist at the same time, one 

 kind then naturally modifying the hue of the other. With 

 such a condition, viz., of different elements associated at 

 the same time in the same flower, one can easily conceive 

 that a plant widely distributed might under different condi- 

 tions in one case develop the purple element which is free 

 in the cell sap, and in another, the fixed yellow xanthophyl, 

 or erythrophyl substance, so that the difficulty of assuming 

 that the colors of different species of the same genus were 

 all derived from one primary color of one original ancestor 

 would be eliminated. 



These pigments are found mainly near the surface of the 

 flower petal, just beneath the cuticle, sometimes in the skin 

 itself. In a white Crocus variegated with purple, if the 

 transparent cuticle is peeled off, it carries the purple color 

 with it, leaving the remaining tissue white ; not infrequently 

 however, the pigment extends quite through the tissue from 

 side to side, continuing even down the peduncle and stem, 

 as in Arethusa and certain Begonias. The yellow Crocus is 

 tinged quite through the entire tissue, also Buttercup, La- 

 burnum, purple Iris and red Pa^ony, Various kinds of 

 acids are found free in the cell sap, or in cond)ination with 

 alkalies, and the varying proportions of these elements play 

 an important part in estaldishing the colors of flowers ; the 

 effect of these will l^e described later. 



As hinted above, there is no good reason for supposing 

 that there was an original color in any genus from which 

 all the colors of the other species were derived. There was 



