vi] INFLUENCING THE FORMATION OF ANTHOCYANINS 85 



is brought about by increase of synthetic products, due to greater 

 insolation by day accompanied by low night temperature, and to 

 stunted growth, rather than to any direct action of light on pigment 

 formation, but at present there is no conclusive evidence. 



In the same way lack of synthetic products due to poor conditions 

 of the plant reduces pigment formation. The experiments of Sachs 

 (271), Askenasy (282), Vochtin-g (325) and Klebs (360), in which leaves 

 of plants were kept in darkness while the flowers were exposed to 

 light, are not so conclusive as those previously mentioned. The method 

 is so drastic, and may influence the whole nutrition of the plant to such 

 an extent, that the non-development of flower-colour cannot be regarded 

 as having any great significance. 



A phenomenon of considerable interest in connection with nutrition 

 and formation of red pigment is that pointed out by Mirande (332) 

 as occurring in the genus Cuscuta, in which anthocyanin is widely 

 produced. From observations made upon the development of many 

 different species of Cuscuta on various hosts, Mirande concludes that 

 the amount of pigment varies not only in different species but also in 

 each species according to the host on which it grows. For instance, 

 the same species growing on Sanibucus nigra (poor) and Forsythia 

 viridissima (rich in sugar) becomes green on the former but very red on 

 the latter. Hence Mirande correctly deduces the fact that not only 

 good development of the parasite but also the formation of red colour 

 is correlated with good nutrition. In nature, species of Cuscuta 

 passing from one host to another are seen to show different amounts 

 of pigmentation. Chemical tests made by Mirande on extracts from 

 the host plants showed that the greatest production of colour was 

 found when the host plants were capable of producing most sugar. 



The conclusions which may be drawn from all the instances quoted 

 above are that an unnatural accumulation of synthetic products may 

 cause colour to be developed in organs not normally coloured. At the 

 same time a good supply of nutrition will intensify colour in parts of 

 plants which are normally coloured. There is reason to believe that, 

 of the accumulated substances, the most potent in bringing about 

 colour production are sugars and glucosides, and this will be found to 

 be borne out by observations connected with the effect of other factors 

 considered in this chapter. Also an increase of the chromogens from 

 which anthocyanins are produced takes place under the conditions men- 

 tioned above. The manner in which glucosides, sugars, chromogens 

 and pigment may be connected is dealt with in the next chapter. 



