476 



Mr. H. C. Sorby on 



[June 19, 



IV. The same plant, in the same spring, where more exposed to light. 

 Y. The same plant, growing in and on the surface of water, where fully 

 exposed to direct sun. 



VI. Probably a different species of Oscillatoria, growing on a damp 

 wall, completely exposed to the sun. 



VII. Peltigera canina, slightly shaded and having much fructification. 



VIII. The same plant, where much exposed to the sun. 





Blue 

 chloro- 

 phyll. 



fucine. 



x nyco* 

 xanthine. 



Orange 

 xantho- 

 phyll. 



XT' 



_r uco- 

 xanthine. 



T • 1 



xanthines. 



1 1 





100 



90 







3 



77 



11 



1? J 





100 



100 







H 



100 



14 





III. 



100 



13 







l 



51 



6 



O 





100 



19 



36 



3 



55 



10 







100 



trace 



67 



25 



11 



9 



V 



VI. 



100 



55 



100 



77 



25 



23 





















VII. 



100 



55 



27 



32 







32 





' VIII. 



100 



55 



54 - 



"100 







100 



















In this Table are compared together the same or very similar plants 

 growing in different conditions, as connected by the brackets, and also 

 plants belonging even to different classes. On comparing together the 

 amount of the different constituents of the same plants grown in less or 

 more light, it will be seen that some of the differences are in perfect 

 agreement with those already described; but the differences in the 

 Oscillatorice are evidently not a mere change in equilibrium, due to the 

 decomposing action of the light, and point unmistakably to a great 

 difference in the constructive force of the plant, depending on increased 

 light. There is a remarkable development of phycoxanthine and orange 

 xanthophyll, and a great decrease in the amount of chlorofucine and 

 fucoxanthine, and the result is that we have a .change almost from the 

 type of olive Algce to that of certain lichens. „ When growing in a very 

 shady place the colouring-matters soluble in bisulphide of carbon are all 

 identical with those in Fticus and other olive Algce, whereas when grown 

 exposed to mnch sun there is a great reduction in the amount of those 

 substances which are so characteristic of , that group, and at the same 

 time a great development of others which are almost or altogether absent 

 from it, but occur in large quantity in, and are very characteristic of, 

 such lichens as Peltigera canina. The olive Algce are, however, di- 

 stinguished from those Oscillatorice which approach them most closely by 

 the absence of the phycocyans ; and though these occur in Peltigera, it 



