THE MUTATED GENE 95 



2. There might be a background effect (just as in many 

 animal colors, e.g., the skin of a tree frog; of course no pigment 

 cells are involved in plants). 



3. There might be the so-called copigment effect, which means 

 that a certain type of pigment is changed in color by the mere 

 presence of another pigment. The pigments involved are (a) the 

 plastid ones, carotin and xanthophyll; (6) the more important 

 sap pigments. The latter fall into two main groups, the antho- 

 xanthins and the anthocyanins. The xanthins have ivory to 

 yellow color and belong chemically to the group of flavones. 

 They may or may not occur as glucosides (containing a sugar 

 residue). They may produce independent color effects, act with 

 a background effect, act as copigments or quantitatively together 

 with the anthocyanins. Their genetic relation to the antho- 

 cyanins will be discussed later. As copigments they have a 

 bluing effect upon anthocyanin. The anthocyanin pigments are 

 sap-soluble glucosides which vary in color from scarlet through 

 violet and purple to blue. Generally, their structure is similar 

 to that of the xanthins, the fundamental differences being the 

 substitution of an O-atom at position 4 in the flavones, as shown 

 below. 



HOr Y V< >OH HO 



CI 

 O 



<3 



OH 



OH 



HO O HO 



Flavone (luteolin) Anthocyan (pelargonidin) 



They fall into three main groups: pelargonidin, cyanidin, and 

 delphinidin types, differing by the possession of 1, 2, or 30H- 

 groups on the side phenyl ring (the preceding formula has one 

 and is a pelargonidin). More than one of these pigments may 

 be present in a plant, and there are numerous chemical variations 

 such as methylation of one or more OH-groups, change's in the 

 sugar residue, and addition of an organic acid. These variations 

 and substitutions are caused by genetic factors. Most important 

 are the sugar residues situated at position 3 or 5. These might 

 be glucose, galactose, cellobiose, and others; <.g., pelargonin, 



