IIARDWICKE'S SCIENCE-GOSSIP. 



121 



THE COLOURS OF LEAVES AND FLOWERS. 



By A. G. TANSLEY. 



N Science -Gossip 

 for last October, 

 appeared an article 

 by Mr. G. W. Bul- 

 man, called "A 

 Red Leaf— A 

 Study in Botany," 

 which I am sur- 

 prised to see has 

 passed entirely un- 

 challenged ; I 

 should therefore 

 like to offer a few 

 remarks upon the 

 subject. 



In this article 

 Mr. Bulman ob- 

 jects to "certain 

 modern botanical 

 theories" by which 

 the colours of 

 flowers are held to be developed through insect 

 selection. His objection is based on the fact that, at 

 various times of the year, leaves also develop brilliant 

 colours. He remarks, very justly, that "we are just 

 as much bound to account for the colours of these as 

 of the varied hues of the blossoms," and he asks 

 whether they can "be shown to be any distinct 

 benefit to the plant in the struggle for existence." 



He then goes on to attack a further development of 

 the evolution of colour theory, viz., that special 

 colours are evolved by, and together with, special 

 insects ; red and blue by bees and Lepidoptera, for 

 instance. His grounds are (i) that (in his experience) 

 there are certain red and blue flowers not visited by 

 bees, and (2) that many flowers of various other 

 colours are visited by these insects. Lastly, he cites 

 two instances (the hawthorn and some Umbelliferae) 

 which he holds to be in contradiction to the " special 

 colour " theory. 



Mr. Bulman's objection to the general theory of 

 colour development in flowers, is, I think, fully 

 met by a quotation on the similarity of the coloured 

 No. 282.— June 1888. 



pigments found in leaves to those of flowers which 

 Grant Allen (" Colours of Flowers," p. 20) makes 

 from Dr. Sorby, the great investigator of the chemical 

 nature of the coloured pigments found in plants. It 

 is as follows : — 



" The coloured substances in the petals are, in many 

 cases, exactly the same as those in the foliage from 

 which chlorophyll has disappeared ; so that the petals 

 are often exactly like leaves which have turned yellow 

 and red in autumn, or the very yellow or red leaves 

 of early spring." "The colour of many crimson, 

 pink, and red flowers is due to the development of 

 substances belonging to the erythrophyll group, and 

 not unfrequently to exactly the same kind as that so 

 often found in leaves. The facts seem to indicate, 

 that these various substances may be due to an alter- 

 ation of the normal constituents of leaves. So far as 

 I have been able to ascertain, their development 

 seems as if related to extra oxidisation, modified by 

 light and other varying conditions not yet under- 

 stood." 



Clearly then, the development of the coloured 

 pigments in both leaves and flowers is due to the 

 same primary chemical set of causes ; but, while 

 more or less accidental (being " modified by light and 

 other varying conditions not yet understood,") in the 

 case of leaves, in flowers the colours are stereotyped 

 and perpetuated by insect selection. To Mr. 

 Bulman's question, therefore, as to whether the 

 colours of leaves can "be shown to be any distinct 

 benefit to the plant in the struggle for existence," I 

 would answer decidedly in the negative ; if the colours 

 were any distinct benefit to the plant in the struggle, 

 natural selection would have seized upon and fostered 

 this peculiarity, and it would have become permanent, 

 instead of remaining a simple chemical outcome of 

 certain processes which take place in leaves in the 

 absence of chlorophyll, and subject to modification 

 by " light and other varying conditions." 



Mr. Bulman further asks, why bees do not visit 

 brilliantly coloured leaves as if they were flowers. 

 The reason appears simple enough. If they ever do 

 visit them, they would soon find that there is nothing 



