1887-88.] Colouring Matters of Leaves and Flowers. 283 



red solid colours, that is between the chloroplasts and the 

 chromoplasts ; as yet, however, we are not certain of a like 

 relationship on the part of the fluid colours. 



Hansen assumes that there are four distinct pigments in 

 plants : — Lippochrome-yellow (etiolin), soluble yellow, flower- 

 red, and chlorophyll-green, and that chlorophyll is not the 

 source of the other pigments. 



The passage of brightly coloured pigments from corpuscles 

 to the condition of that of cell fluid has been clearly 

 demonstrated. The transitions and gTadations in colour 

 observable between green leaves and red bracts or flowers 

 point to a common origin of the pigments, if not in the 

 chlorophyll, possibly in the etiolin ; but it is possible, never- 

 theless, to imagine that a red pigment may be directly 

 produced instead of arising as a transition form out of 

 etiolin. 



It is necessary to remember that, as asserted by Vines, the 

 fluid colours, allied to the aromatic group of substances, are 

 physiologically waste products. 



We shall regard them as definitely related to the chloro- 

 phyll colours — chlorophyll itself being produced when the 

 metabolism is constructive ; red or other colours when it is 

 destructive. Instances of this we shall deal with when con- 

 sidering colour-changes. 



Part II. 



Colour- Changes. 



Colour-changes may be, perhaps, most suitably considered 

 under the following heads : — 



1. Those induced artificially by various reagents; and those 



induced naturally, by the presence of substances of 

 a like nature in the cells of the living plant. 



2. Those associated with particular environments ; which 



environments are either dh-ectly or indirectly the 

 cause of change. 



3. Those characteristic of definite conditions of growth. 



(These conditions may or may not be evidently refer- 

 able to the influence of special environment.) 



