266 PROCEEDINGS OF THE AMERICAN ACADEMY 



4. In the generality of cases coloring matters, such as indigo, 

 Indian yellow, madder-lake, and the like, do not separately exist in 

 the substance of vegetables, but the pigments are disengaged through 

 fermentation or oxygenation. Again, alizarin itself is reddish yellow, 

 but alkaliue solutions strike it a rich violet, just as we find them act 

 towards the substance which Mr. Sorby calls Aphidilutein. 



5. Mr. Sorby's four stages of the changes effected by tlie oxidation 

 of Aphideine produce four different substances. 



The different colors produced by the uoe of different chemicals 

 must be compared in Mr. Buckton's paper. But there can be no 

 doubt that here colors are produced chemically out of protein-bodies, 

 — a fact somewhat homologous to the before-quoted artificial pro- 

 duction of indigo. 



The influence of temperature on the colors of the imago of Lepidop- 

 tera was first shown by Mr. Dorfmeister. He proved that a higher 

 temperature changes the reddish-yellow of the hind-wings of Bombyx 

 caja to minium, a lower temperature to ochreous yellow. The chan- 

 ging of spring-races of butterflies into autumn-races by putting the 

 chrysalis on ice, the well-known experiments made by Mr. W. H. 

 Edwards and Prof. Weismann and others, show unquestionably the 

 influence of temperature on colors. Probably here the change is the 

 effect of a surplus of nitrogen. The water absorbs a small quantity 

 of air, but in such a manner that this air contains less than two 

 parts (1.87) of nitrogen to one part of oxygen, instead of four parts 

 of nitrogen. Therefore an excess of nitrogen in the surrounding air 

 must be the consequence, as is the case in the iced chambers of 

 fi-uit-houses, where the oxygen is purposely rarefied in relative 

 quantity. By this nitrogen, together with the nitrogen contained 

 in the chrysalis, life and development are retarded to a minimum ; 

 but the chemical action which produces colors will work neverthe- 

 less to a certain extent. Therefore a change in the colors of the 

 imago is the necessary consequence, and this change affects proba- 

 bly the pattern, which is, as stated before, produced largely by 

 oxygen, which is here rarefied. 



Goethe has characterized the yellow and related colors as acid 

 ones, the blue and related as alkaline colors. He states that vege- 

 table yellow colors can be changed by alkali into red, or even into 

 blue red. 



For plants the predominant color is green, for insects bi'owu ; both 

 of which are called indifferent colors. 



