200 ANTHOCYANINS AND GENETICS 



THE EFFECT OF OUTSIDE FACTORS ON COLOUR- VARIATION. 



It has very often been stated that the colours of flowers are affected 

 by the soil in which the plants are growing, and the belief is still prevalent. 

 In any discussion upon the subject we generally meet with one or other 

 of two illustrations of classical interest. One is the change of colour 

 in Hydrangea (or Hortensia) flowers when the roots are supplied with 

 some form of iron or aluminium salts; the other is the 'zinc Violet' 

 which is a blue-flowered form of Viola lulea. This variety grows in 

 a soil containing as much as 20 % zinc oxide, and in the ash of the 

 plant may be found 1 % zinc oxide. Hence the idea arose that the 

 'zinc Violet' might derive its blue colour from the presence of zinc in 

 the tissues. The effect of soils on Hydrangea must have been noticed 

 at a very early date, for Schiibler & Lachenmeyer (429) in 1834 gave an 

 account of analyses of soils which change the colour of the flowers. 

 Trials have been made from time to time with other chemical substances 

 upon other plants, but no striking results have been obtained. In 

 view, however, of the value attached to such results, it may be well 

 to give an account of some of the experiments. 



As regards the 'zinc Violet,' Hoffmann was led to conclude that 

 the presence of zinc had no influence on the colour, because, w T hen 

 transferred to another soil which did not contain zinc, the blue colour 

 remained ; the colour, moreover, may vary even when the soil contains 

 zinc. Though practically only confirming the fact that colour-changes 

 in Hydrangea are brought about by iron and aluminium salts, the 

 work of Molisch (467) in this direction is important, since he treated 

 the subject on an experimental basis. His method was to grow 

 Hydrangea plants in pots and to mix with the soil the substances of 

 which he wished to test the effect. The following table will give a general 

 idea of his results: 



Substance added to soil Colour of flowers Remarks 



Normal soil ... ... Red 



Aluminium sulphate ... Strongly blue ... Leaves became brown in 



some cases and died 

 Common alum ... ... Blue, sometimes bluish 



A1 2 (S'O 4 ) 3 + K 2 SO 4 + 24H 2 O sometimes pink with 



blue filaments 



Ferrous sulphate Pink, bluish, or blue... In most cases, after a 



few days, the leaves 

 turned brown and com- 

 menced to fall off 



