vi] INFLUENCING THE FORMATION OF ANTHOCYANINS 93 



Effect of sugar-feeding. 



The term sugar-feeding means that the plant is supplied artificially 

 with extra amounts of sugar. In the case of floating or submerged 

 water-plants, the whole plant can be immersed for experiment in dilute 

 sugar solution ; in the case of land plants, the stems of leafy branches, 

 or the petioles of isolated leaves, can be put in the solution; or the 

 leaves can be cut into pieces and floated in the liquid. 



The first investigations of the results of this process were carried 

 out by Overton (333). While conducting some experiments on osmosis 

 with Hydrocharis Morsus-ranae, Overton noted that the leaves of this 

 plant tended to become red when the plants were grown in 5 % cane 

 sugar solution. Later, the idea occurred to him that autumnal colora- 

 tion might be due to excess of sugar in the leaf tissues, and he claims to 

 have shown that autumnal leaves contain more sugar than green leaves. 

 On the basis of this idea, he then commenced some systematic investi- 

 gations on sugar-feeding with a view to gaining more knowledge of the 

 whole phenomenon. 



Experiments were first made with Hydrocharis plants grown in 

 various solutions, and the results were as follows : 



Hydrocharis Morsus-ranae. Plants in 2 % invert sugar showed 

 excess of anthocyanin over the control in four days. This was true 

 of pigment in all parts leaves, petioles, stolons and roots, and the 

 intensity of pigmentation increased with time. In 2 % cane sugar 

 the results were similar. 



Plants in both the above solutions flowered rather earlier than control 

 plants, but the flowers were unaffected by the cultures. 



In 2 % glucose there was the usual reddening ; also in 2 % laevulose. 

 In 2 % galactose there was no reddening, and in 5 % lactose, the 

 reddening was very slight. In 2 %, 4 % and 10 % glycerine, no colour 

 developed ; this was also the case in solutions of potassium nitrate, 

 sodium chloride, sodium sulphate and of other salts. 



In 3 % invert sugar in a dark room there was no trace of reddening. 



Microscopically it was found that colour was produced in the meso- 

 phyll cells, and never in either the upper or under epidermis. 



The following species were also used: 



Elodea canadensis. In 2-3 % invert sugar, a reddish colour developed 

 in the younger leaves. 



Vallisneria spiralis. In sugar cultures there was an increase of red 

 colour which was located in the epidermis as well as in the inner tissues. 



