AS A SPECIPIC CHABACTEE IK LICHEKS. 43 



solution is immaterial, so long as it is not so strong as to destroy 

 the red colour at the very moment of its formation. It is suffi- 

 cient that "we employ the same solution (as to strength) in 

 every case as a standard of comparison. The medium in which 

 the colorific principles of the lichen should be dissolved * for the 

 due exhibition of the red reaction varies in different cases. In 

 some instances a simple aqueous infusion may suffice j in others the 

 comminuted lichen must be boiled in various solvents ; while in 

 others, again, a lime solution is apparently the most suitable. The 

 medium, however, which is of most general application is alcoJiol f, 

 in the form of ordinary spirits of wine. It is especially useful and 

 convenient in experiments on the small scale. I have employed 

 it now in nearly 300 test-tube experiments, boiling the pulverized 

 or chopped lichen for a few minutes in a little alcohol; and I 

 have seldom failed to observe, in greater or less quantity, a whitish 

 or variously-coloured gelatinous extractive J, which appears to 

 consist, in great measure, of the colorific principles of the plant. 

 The bleaching-solution test, though extremely convenient and 

 applicable in the generality of cases, cannot in every instance be 

 relied on, either as a quantitative or qualitative indicator of the 

 presence of colorific materials capable of yielding by ammoniacal 

 maceration red or purple dyes. In other words, the action of the 

 test appears to be irregular or capricious, perhaps from being 

 sometimes chemically inappropriate. I have found, for instance, 

 that bleaching-solution struck no red with an alcoholic solution of 

 lichens which, macerated in the usual way in a weak ammonia- 

 cal liquor, yielded a well-marked beautiful red dye; while, on tlie 

 other hand, a red reaction was developed in some cases in which, 

 under the same conditions of experiment, I have failed to obtain 

 an archil. The irregularities in question may depend on 

 " 1. Inaccuracy or carelessness in manipxdation. 



" 2. Alcohol not being the suitable solvent of certain colorific 



principles. 



" 3. Ammoniacal maceration not being the proper means of 



developing an archil. 



* The colorific matter of Lichens is extractable with rerj different degrees of 



facihty by different solvents. 



t The difficulty of applying bleaching-solution directly to the thallus, and 

 the fact that its reaction is best manifested in solutions of colorific principles, 

 are arguments for preferring the use of alcoholic decoctions, 



% Assxuning the character of a mucous flocculence or precipitate. 



