308 ANNUAL HECORD OF SCIENCE AND INDUSTRY. 



yellow colors, some so pale as to be nearly colorless, and oth- 

 ers of a fine dark golden yellow. They are soluble in water, 

 in alcohol, and in ether, but not in bisulphide of carbon. Of 

 these there are two sub-groups, one in which a dark color is 

 produced with ferric salts, constituting the tannic acid sub- 

 group, and the other giving no such reaction, and forming 

 the chrysophyl sub-group. In both sub-groups the intensity 

 of color is usually greatly increased by partial oxidization, 

 and they are thus altered into colors of the following group. 

 Fifth, the phaiophyl group, which comprise a number of col- 

 ors insoluble in bisulphide of carbon, and of very variable 

 solubility in water or alcohol. These are in that state of oxi- 

 dization which has a maximum intensity of color, and are sim- 

 ply decolorized by further oxidization. Our author proceeds 

 to state that the numerous tints of foliage depend almost en- 

 tirely on the relative and absolute amount of the various col- 

 ors of these different groups, although all their relationships 

 can not at present be explained. 



The color of green leaves is mainly due to a mixture of 

 chlorophyl and xanthophyl, and the variation in the relative 

 and absolute amount of these easily accounts for the darker 

 and brighter greens. The tints are also much modified by 

 the presence of colors of the erythrophyl group, which, ac- 

 cording to circumstances, may give rise to lighter or darker 

 browns, approaching to black or to reds. Healthy unchanged 

 leaves also contain various substances belonging to the chrys- 

 otannic group ; but in many cases, when these belong to the 

 more typical kinds of tannic acid, their color is so faint that 

 they have little or no influence on the general appearance of 

 the leaves. 



On the approach of autumn, before the leaves have with- 

 ered, the foliage of different plants presents an exceedingly 

 variable mixture of chlorophyl, xanthophyl, and erythrophyl, 

 with the different members of the chrysotannin group, and it 

 is to the changes which occur in some or all of these sub- 

 stances that the very variable tints of autumn are due. The 

 most striking of these depend on the alteration of the chlo- 

 rophyl. 80 long as it remains green the production of the 

 bright reds and yellows is impossible ; but when it disap- 

 pears, the yellow color of the xanthophyl is made apparent, 

 and if much erythrophyl be present or contemporaneously 



