M. Wheldale 137 



The local appearance of pigment in various plant tissues thus 

 resolves itself into a matter of local variations in the concentration of 

 sugars and glucosides in the tissues. 



In order to test the validity of the hypothesis as stated above, it 

 must be ascertained whether the conditions which give rise to forma- 

 tion of pigment are such as would influence the amount of glucosides 

 and sugars present, and in this way it should be possible to demonstrate 

 a connection, if it exists, between the two phenomena. 



I have classified my evidence from various sources under the 

 following headings : — 



(1) Analogous reactions. 



(2) Distribution of anthocyanin. 



(3) Concentration of sugars and glucosides in various tissues. 



(4) Existence of enzymes. 



(5) Sugar-feeding. 



Evidence from Analogous Reactions^ 



Many of the reactions involved in plant metabolism are known to 

 be of a reversible or balanced nature. Excess of sugar, for instance, 

 may be converted into starch and thereby stored up in an insoluble 

 form which is again hydrolysed into sugar when required. Similarly 

 oils may be hydrolysed into fatty acids and glycerine, and these products 

 again synthesised into oils. Synthesis and hydrolysis are also con- 

 tinually taking place between the disaccharides and the monosaccha- 

 rides. Cane-sugar is synthesised from glucose and fructose and 

 hydrolysed into the same products: dextrose is synthesised into maltose 

 which is hydrolysed into dextrose and so forth. 



As a typical reversible reaction we may quote the hydrolysis of 

 ethyl acetate. When ethyl acetate is treated with water, hydrolysis 

 into acetic acid and ethyl alcohol commences at once, but as soon as 

 any products of hydrolysis are formed, the reverse action is also set up, 

 namely the synthesis of ethyl acetate from acetic acid and ethyl 

 alcohol. Hence in any mixture of the four substances, ethyl acetate, 

 acetic acid, ethyl alcohol and water, two opposite reactions will proceed 

 at diflferent rates : — 



Ethyl acetate + water - ^ ethyl alcohol + acetic acid. 



1 In connection with enzyme action I have freely qnoted from Bayliss, The Natwre 

 of Enzyme Action, 1908. 



Jonm. of Gen. i 10 



