1887-88.] Colouring Matters of Leaves and Flowers. 301 



cases of colour-transition to which (in Part II.) I drew atten- 

 tion are capable of an houiologovis explanation in agreement 

 with the explanation so far given of autumn and spring-colour 

 and that of reproductive axes. 



Thus colour appears, or undergoes change, in 



(1) Parts farthest from the supply of nutrition, where 

 there is either less material for elaboration, or where more 

 elaboration has been undergone by the coloured sub- 

 stances. 



Ex. — This increase in colouring may be seen in single 

 inflorescences even, tips or whole rays of Compositce, in 

 Silene, &c. (Pellat) ; exterior of fruits, as apples ; this especi- 

 ally on — 



(2) The sunny sides, where the cells are exposed to influ- 

 ences which will quicken or increase the metabolic changes 

 in the cell-contents ; also indii-ectly seen in effects of light, 

 heat, and soils. 



Ux. — Exteriors of roots and seeds (turnip root). 



(3) Where growth is evidently effected at the expense of 

 stores of material, as in tubers and shoots from perennial 

 root-stocks — AsjKiragics, Lapageria. 



(4) Lower colours of these series of colour-products are pro- 

 duced in place of higher products, as in albinism, and blanching 

 from weakened constitution, implying a less vigorous vitality, 

 and less material assunilated which will give brilliantly 

 coloured products. 



(5) Colour in flowers during their growth when opening, 

 or before death, occurs with greater or less brilliancy as the 

 metabolism is hastened or not. 



(6) Colour results directly from various chemical actions 

 artificially or naturally observed, of which cases, that where 

 it is a result of oxidation (reds from yellows, and deeper 

 colours from the reds) affords the clearest evidence of 

 destructive metabolism. 



We must, of course, leave it to the chemist or the physi- 

 cist to decide as to whether the later coloured products are 

 in themselves more complex, or due to a splitting up into 

 simpler substances ; or whether, as suggested by Piussel and 

 Lapraik, the colour-changes observable in most cases with 

 such different reagents are due to molecvdar rather than 

 chemical alteration of the substance. 



