M. Wheldale 147 



That a relationship exists between pigmentation and assimilation is 

 further borne out by the appearance of anthocyanin in old leaves, 

 variegated leaves (with parts free from chlorophyll), autumnal leaves, 

 leaves exposed to drought or low temperature and in flowers and 

 ripening fruits. In all these cases the same difficulty arises as to the 

 real cause, since the starch-forming power may be diminished as well 

 as the assimilative. Starch does not as a rule appear in petals ; and in 

 fruits the colouring matter is often limited to the epidermis and sub- 

 epidermal layers which are free from starch though the flesh of the 

 fruit may be full of starch. In variegated leaves the chlorotic portions, 

 in which pigment often appears, are unable to form starch. I have 

 made a number of observations upon the starch contents of green leaves 

 and of leaves, from the same plant, reddened as a result of cold, 

 drought, etc., and I have found the red leaves almost invariably to 

 contain less starch than the green. 



It must also be borne in mind that the translocation of both sugar 

 and glucosides may be hindered by low temperature, drought, age, etc. 

 I am inclined to believe, in the absence of more direct evidence, that 

 the reddening under these conditions is due to diminished translocation 

 of glucosides combined with increased formation of these substances 

 due to the presence simultaneously of excess of siigar. 



Results lately published by Combes (3) corroborate this view to some 

 extent. Combes has made comparative estimations of the glucosides 

 and sugars in both red and green leaves of Ampelopsis hederacea in 

 which reddening was due to light intensity, and in Rosa canina, 

 Mahonia aquifolium and Sorbus latifolia showing autumnal colouration. 



His results may be expressed as follows : — 



From these numbers we see that the concentration of glucosides 

 and sugars in red leaves is greater than in green, that of dextrins 

 greater in green than red, whereas the amount of insoluble carbo- 



