280 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



pigment, whilst disappearance of the red colour followed 

 upon an increase in temperature. 



It was later demonstrated by Eberhardt (1903) that 

 greater quantities of the red colouring matter were present 

 in plants exposed to dry air than in similar ones in air of 

 a normal degree of humidity. 



The effect of the addition of various sugars to the culture 

 medium was investigated by Overton. When in sufficient 

 quantities, glucose, fructose, and sucrose, all induced the 

 formation of anthocyanin in plants in which the pigment 

 was normally located in the mesophyll, but failed to do 

 so in those in which it was in the epidermis. This effect 

 was due to the chemical action of the sugars, not to their 

 osmotic pressure, since salt solutions isotonic with them did 

 not lead to the development of a red colour. 



In the course of his researches on the respiratory chromo- 

 gens, Palladin (1908), too, found that exposure to light 

 resulted in the production of more anthocyanin in frag- 

 ments of the leaves of Rumex patientia placed in 20 per 

 cent, sucrose solution than was formed in similar portions 

 kept in the dark. The latter, however, did contain some 

 red pigment, whereas controls in water were entirely devoid 

 of anthocyanin. The respiratory chromogens also were 

 present in large quantity in the illuminated cells, in smaller 

 quantity in those in the sucrose solution which were main- 

 tained in the dark. In the control they could still be 

 detected by the addition of a peroxidase and peroxide, 

 but the amount was much reduced. 



That the presence of light is not absolutely necessary for 

 the formation of anthocyanin was further illustrated by the 

 work of Chartier and Colin (1911), for they found that the 

 red root-tip of the seedlings of certain Crassulaceae still 

 showed the colour when grown in complete absence of 

 light. Various experiments of Moreau quoted by these 



