146 ANTHOCYANINS AND GENETICS 



anthocyanin pigments, and may (with a certain exception in 9) take 

 place simultaneously with variation in the anthocyanins. 



6. The loss of power to produce yellow pigment in the plastids. 

 The type has yellow plastids: the variety colourless plastids. 



7. The loss of power to inhibit the formation of pigment in the 

 plastids. The type has colourless plastids : the variety yellow plastids. 



8. The loss of power to inhibit the formation of yellow soluble 

 pigments. There is no yellow in the type: the variety is yellow. 



9. The loss of power to produce yellow soluble pigment. This 

 variation is of rare occurrence. The type may contain both yellow 

 soluble pigment and anthocyanin, and the variety may be without one 

 or both : or the type may be without yellow colour, but may produce 

 a soluble yellow variety, which, in turn, may lose its power of forming 

 yellow pigment and is then also unable apparently to form anthocyanin. 



It should be understood that the above is only a classification on 

 the broadest basis ; when we come to the details of variation it is almost 

 necessary to consider each case separately. It is difficult, for various 

 reasons, to make any kind of comprehensive classification, apart 

 from the fact that no two cases are exactly alike; in many species, 

 for instance, the inheritance of colour has not been systematically 

 worked out, and relationships between variations cannot be correctly 

 judged; new 'breaks/ moreover, are continually occurring in horti- 

 cultural plants; there are also the complexities introduced by species- 

 crossing, and in these circumstances it is often difficult to identify 

 the type from which the variety has arisen. In the following paragraphs 

 an attempt is made to indicate some of the main series or ranges of 

 variation. It has only been possible to include a selection from the 

 great mass of material provided by observations on plants under 

 cultivation, but it is hoped that the lines suggested may provide a basis 

 for further classification, as our knowledge of the inter-relationships of 

 varieties increases. 



A point to be emphasised is that one cannot judge correctly of the 

 inter-relationships of varieties from appearances. For true knowledge 

 it is not only necessary, as we have said, to find out the behaviour 

 of the pigments in heredity, but we must examine their properties, 

 and above all we should know their chemical composition. The colour 

 series in Dahlia and Tropaeolum, for instance, are similar to the eye, 

 but are really fundamentally different. Hence, in the following series, 

 from lack of knowledge, instances may be grouped together which are 

 not in reality of the same nature. 



