284 Mr Philip Sewell on the [sess. lii. 



1. The colours produced from chlorophyll by means of 

 various reagents, either in the cells of the plant or in solu- 

 tions, have been numerous enough to lead to the assertion 

 that, " given a solution of chlorophyll, it is possible by means 

 of acids and alkalies to produce all the colours exhibited by 

 flowers and fruits." 



It does not concern us to know whether such colours are 

 produced by decomposition or (as is probable at times) 

 whether they exist mixed with the chlorophyll in the plant 

 (a question which was alluded to in the first part of this 

 paper), but we may notice in detail various of the ways in 

 which such changes may be brought about. 



(A) They may result from mere mechanical separation — 

 for instance, by solvents such as fresh water, borax-water, and 

 alcohol, by which means, among the Florideae, Fucacese, &c., 

 brown and red colours, normally obscuring the chlorophyll 

 present, may be quickly dissolved out. Among the Diato- 

 maceae, the normal yellow colour due to the presence of 

 phycoxanthine- gives place under such agents to green, as 

 this substance is affected more quickly than is the 

 chlorophyll. 



(B) That oxidation or reduction may also produce colour- 

 change, we have evidence alike in nature and by experiment. 

 Sorby some time ago asserted that by oxidation yellow 

 changed to red, and red became l^rown, and if the process 

 be carried further, the coloured substance may totally dis- 

 appear. Timiriazeff' has shown that chlorophyll may be 

 rendered red, and finally colourless, l)y reduction (with 

 nascent hydrogen), and regain its colour on oxidation. 

 Another example of such induced change to and from 

 green is that afforded by the experiments of Wiesner and 

 Lindt \\\)(m NcoUia 7iich.is-avis. In this plant the transforma- 

 tion of the brown corpuscles to green may be brought al)out 

 by an iMcreaso of tenqjerature ])y addition of alcohol, or, most 

 ra))idly of all, by the action of an aldehyde as a reducing 

 agent. 



(C) Very many reagents (iodine-water and chloride of 

 zinc, HCl, &c.) will re-convert yellow corpuscles to green, 

 the colour at times Ijeing permanent, at timers transitory. 



As similar colours appear witli widely did'cnsnt reagents, 

 and as the variisty of these clianges is so great, Kussel and 



