96 PHYSIOLOGICAL CONDITIONS AND FACTORS [CH. 



epidermal cells. But if in normal circumstances the pigment is formed 

 in the inner tissues, then sugar-feeding (especially with fructose and 

 glucose) produces red pigment in a high percentage of cases, and this 

 pigment is localised in the mesophyll and not in the epidermis. 



Overton also tried the effect of putting the inflorescence of white- 

 flowered varieties into sugar solution. Thus, for instance, the 

 inflorescence stalk of white Pelargonium zonale was placed in 3 % 

 solution of invert sugar, but no trace of red colour was formed in the 

 flowers though the stalk showed reddening. Negative results were 

 also obtained with Anemone japonica. Overton concludes that some 

 other factor, apart from presence of sugar, is necessary in these cases. 



Further researches on sugar-feeding were made some years later 

 by Katie (354), and of these the experiments on Hydrilla verticillata 

 (Hydrocharitaceae) are given in the greatest detail as follows: 



Inorganic culture media containing various salts of potassium, sodium, 

 calcium, magnesium, ammonium, iron, aluminium and lithium had 

 practically no effect on the formation of pigment. In glucose (-05-3 %) 

 solutions, red pigment was formed in the light and in the dark, and in 

 isolated leaves more quickly than in pieces of leafy stem. In laevulose 

 (1-5 %) and cane sugar also pigment developed both in the light and 

 in the dark, but the cane sugar (of concentration -5-25 %) was most 

 favourable to reddening. Only a slight coloration appeared with maltose 

 (1-3 %) both in the light and in the dark. In lactose (1-5 %), raffinose 

 (1-10 %), inulin (1-3 %) and glycerine (4-5 %) pigment was formed 

 only in the light. Some colour was developed in (1-4 %) ethyl alcohol 

 and in mannite (1-2 %), but none in galactose (up to 5 %), arabinose, 

 formol (-001 %), dextrin, salicin or asparagin. 



The effect of mixed solutions of carbohydrates and various salts, 

 such as those mentioned above, was tried. It was found that potassium 

 nitrate and mono-potassium phosphate quickened the formation of 

 pigment in sugar solution. Various other potassium salts (except 

 potassium bichromate) had the same effect in a less and varying degree. 

 Katie is of the opinion that the effect of potassium salts is chemical 

 and not osmotic. Sodium salts, on the whole, were found to have 

 little effect; magnesium sulphate and nitrate some positive effect; 

 calcium salts (except CaH 4 (P0 4 ) 2 ), aluminium sulphate, ferric chloride 

 and some ammonium salts a preventative effect. 



Various alkalies, sodium carbonate, potassium hydroxide, calcium 

 hydroxide and magnesium oxide were tried with sugar solutions; the 

 result was to quicken the formation of anthocyanin. Acids, as for 



