ANTHOCYANINS AND GENETICS 217 



R factors, and (3) those which intensify or diminish a reaction, such 

 as colour-formation, which is already in being in the plant, as for 

 instance the De and Di factors of Lathy run. 



It is worthy of note that of all factors it is more often the actual 

 colour-producing factor which gives rise to a heterozygous form ; apart 

 from Mirabilis, the factor for chromogen is unaffected by the hetero- 

 zygous condition, and the same can be said for the factors for concen- 

 tration and dilution. When we learn more of the reactions taking 

 place, we may find that this point has some considerable significance. 



Though we now know something of the material to be employed 

 for research and the methods to be adopted for finding out the cause 

 of colour variation, we cannot add very much to the excellent account 

 and statements by Hopkirk (428) in his Flora Anomoia published in 

 1817. "An astonishing number," he says, "of varieties of colour 

 and its different combinations, have been produced in flowers, especially 

 in the Pink, Carnation, Hyacinth, Anemone, Ranunculus, and Tulip, 



'and while they break 



On the charm'd eye, th' exulting Florist marks 

 With secret pride the wonders of his hand.' 



"The causes of these variations in colour, are at present unknown, 

 some peculiar circumstances in the soil, or the different combinations 

 with oxygen, with acids, or with alkalies, may tend to produce them, 

 but we often find that in the same soil, and under the same manage- 

 ment, one plant always retains its colour, whilst another will most 

 readily acquire a new one." 



We can however say now that the soil does not bring about genetical 

 variation in flower-colour. In the case of Hydrangea, no doubt, the 

 colour is modified by the iron and aluminium salts absorbed by the 

 plant, and the same kind of phenomenon may happen in a lesser degree 

 in other plants. But a continual supply of salts is needed to keep 

 up the variation ; failing this, the red colour returns ; nor does the 

 plant transmit this acquired character of blueness to its offspring. 



