ANTHOCYANINS AND GENETICS 203 



of aluminium salts (potassium alum and aluminium sulphate) : (2) what 

 amount of salt is sufficient to bring out the blue colour without injury 

 to the plant. His methods were to water plants with -5 %, 1 %, and 

 3 % solutions of potassium alum and aluminium sulphate respectively. 

 His results show that cultures watered with 3 % potassium alum 

 produced the finest blue colour, though the leaves were affected with 

 brown spots. The 1 % cultures he regarded as best, since the plants 

 were quite sound, and there was at the same time almost complete 

 blueing of the flowers. This was true for the same concentrations of 

 aluminium sulphate, but the blue coloration was weaker. Hence Vouk 

 does not agree with Molisch that aluminium sulphate has a better 

 effect on the blueing than alum, but he maintains that the latter salt 

 gives the most intense results. His experiments, moreover, show that 

 the change of flower-colour depends, not only on the quality, but also 

 the quantity of the salt used. Other experiments of a similar nature 

 were tried with Phlox decussata but with no result. 



Thus we may conclude that, with the exception of Hydrangea, there 

 is no experimental evidence for the belief that chemical substances 

 in the soil can materially affect flower-colour. There are accounts of 

 various experiments where dyes have been employed, by means of 

 root absorption, for colouring flowers, but the results are purely tem- 

 porary and negligible as far as scientific interest is concerned. We may 

 in this respect well agree with Nehemiah Grew (1) when he remarks: 

 "From what hath been said, we may likewise be confirmed in the 

 use of the already known Rules, and directed unto others yet unknown, 

 in order to the variation of the Colours of Flowers in their Growth. 

 The effecting of this, by putting the Colour desired in the Flower, into 

 the Body or Root of the Plant, is vainly talked of by some : being such 

 a piece of cunning, as for the obtaining a painted face, to eat good 

 store of white and Red Lead." 



Another set of experiments concerned with changes in flower-colour 

 though involving a different external factor, viz. insolation, are those 

 of Rawson (519). These experiments have been conducted upon 

 Tropaeolum plants growing in South Africa and the principle followed 

 was "to shade off with a perfectly opaque screen all direct rays of the 

 sun for certain intervals of daylight." Otherwise there was no other 

 special treatment. By this means Rawson claims to have changed 

 ordinary scarlet and orange varieties into a new mauve variety, and 

 "no known instance occurred of its reverting to the original. Experi- 

 ment so far goes to show that seeds from it after the second year may be 



