Proceedings of the Royal Society of Edinburgh. 317 



A table was also presented, exhibiting the general facts relative 

 to the power of sulphurous acid in decolorizing the Chromnles of 

 plants. This acid, whether employed in its gaseous or liquid 

 form, does not decolorize the Chlorophyle of leaves. It does not 

 affect white flowers. It did not decolorize any one of about a 

 score of yellow flowers submitted to its action. Of thirty or 

 forty red flowers it decolorized all, with the exception of two or 

 three. Of twenty blue flowers, two, the Commelina ccerulea^ and 

 the blue Centaurea Cyanus, resisted its blanching power. It deco- 

 lorized some of the orange-coloured flowers, but rendered others 

 of them of a bright yellow: it decolorized all the purple flowers 

 that were tried, with the exception of purple Centaurea Cyanus, 

 which it rendered blue, and the purple Scabiosa atropurpurea^ which 

 it reddened. It aff^ected the tinted Chromule occurring in other 

 parts of plants than blossoms ; it completely blanches the internal 

 leaves of the red cabbage, which are of a bright purple red, while 

 it renders the external bluish-purple leaves green. It turned to 

 green various leaves, which possessed red tints, whether general 

 over the whole leaf, as the red beet, or partially diffxised, as in some 

 species of Dracaena. It decolorizes some fruits, while others resist 

 its action. 



Along with the general facts, the vai'ious hypotheses respecting 

 the origin of the difl^erent Chromules, and sources of the differences 

 amongst them, the autumnal coloration of leaves, &c., were brought 

 under consider.ition. 



Lastly, a detail was given of the influence of light in the produc- 

 tion of different Chromules, shewing that it is indispensable for the 

 production of the Chlorophyle of leaves, and the tinted Chromules 

 formed during the autumnal coloration of the same parts ; and that 

 it is not indispensable for the formation of some of the finest tints 

 of flowers and fruits, if essential for any. 



The paper terminated with the following general conclusion : 

 That there exist in plants two distinct colourable principles, two 

 species of Cbromogen, one which generates red compounds with 

 acids, and denominated Erythrogen ; and another which forms yel- 

 low compounds with alkalies, called Xanthogen. That these two 

 principles occur together in red and blue flowers, and in the leaves 

 of a few plants which exhibit the former of these tints ; that all 

 green leaves, all white and all yellow flowers, and white fruits, con- 

 tain Xanthogen alone ; tliat Litmus abounds in Elrythrogen, but has 

 no Xanthogen ; that the Chromules of different tints may be gene- 

 rally considered distinct vegetable principles, or compounds having 

 their own proper hue ; sometimes intimately blended, or chemically 

 combined with Chromogen; at other times having no connexion 

 with it ; that they are also occasionally, but not frequently, com- 

 pounds of Chromogen with acids or alkalies. 



The second part of the paper will comprehend an inquiry into 

 the special character and properties of the two colourable principles, 

 the Erythrogen and Xanthogen. 



VOL. XX7. NC. XLIJ. — OCTOBER 1836. Y 



