1887-88,] Colouring Matters of Leaves and Flowers. 293 



duction (as in Ccntaurca Cyanus, for instance) of two or 

 three distinct colours on different branches from the same 

 root-stock. 



In any case, whatever may be the exact difference between 

 the nature imparted to one or another ovule in the same 

 capsule, we have seen sufficient to warrant the assertion that 

 a more or less vigorous assimilation, a stronger or weaker 

 constitution, and even environment directly, do much to 

 influence colour, and this at times to a very marked extent. 



When once we may reasonably account for colour- varia- 

 tion in individual seedlings, it is easy to see how, from the 

 continuance of a particular environment, and also by the 

 influence of the important factor selection, particular colours, 

 or colours related to one another in a series, may become 

 prevalent in natural groups, either among the species of a 

 genus, the genera of a natural order, or, further still, among 

 the natural orders of any alliance. 



Paet hi. 

 Hypotheses accounting for Colour. 



Having recognised the various colour- changes that com- 

 monly occur under conditions, the general effect of which 

 upon the life-processes of the plant is more or less known, 

 we must now acquaint ourselves with the various hypotheses 

 which have been put forward to account for such phenomena. 

 It is not necessary that we should know as to the exact 

 manner in which vibrations of certain wave-lengths are 

 returned to the eye from the various coloured fluids ; this 

 essentially is a question for the physicist. 



A colour-change in certain inorganic bodies (therefore 

 called " metachromes "), from red to violet as they contract, 

 and from violet to red as they expand, or as they become 

 more charged electrically with the negative element, was 

 instanced in Nature some years ago by a physicist, as 

 possibly throwing light on the phenomena of flower-colour. 

 This was in connection with a paper on " The Seasonal Order 

 of Colours in Flowers," also contributed to Nature by Dr 

 Buchan, at that time president of this Society. Dr Buchan 

 observed that of the British plants which flowered between 



TRANS. EOT. SOC. VOL. XVII. U 



