312 NEW PUBLICATIONS.
scopical or internal, too little of general or external, characters. In par- ticular, too much consideration is given in classification to the character of the sporidla [which, by the way, in Leighton's ' Lichen-tlora ' are called spores, — a term of doubtful propriety, considering the close alliance be- tween Fungi and Lichens, and the desirability of a uniform nomenclature of the same classes of organs or bodies in these two great cryptogam ic families] ; too little allowance is made for the wonderful variations of the sporidla in many, if not most. Lichen-species.
Chemical characters are, however, the last fashion of the day among lichenographers. After having differentiated species and genera to a mis- chievously elaborate extent, according to the varying characters of the sporidla, they are being further subdivided according as the thallus, apo- thecia, or hymenial gelatine give this or that reaction with hydrate of potash, hypochlorite of lime, or solution of iodine. \\\ no work that has come under our notice is so much attention devoted, we believe un- necessarily so, to these so-called " chemical characters " as in Leigh- ton's ' Lichen-flora.' Thus he subdivides the genus Cladonia according to the very variable chemical reactions of its species. By such characters he separates sylvatica from rangiferina, and pnngens from furcata. For a similar reason he divorces cana horajul/ata in the genus Alectoria I The specific diagnosis of Pertusaria faginea, L., is based on chemical reactions alone, for we are told " spores not seen " (p. 242). Some of the marked irregularities of chemical reaction in Lichens, as applied to the diagnosis or definition of species, he himself not only admits, but is compelled to point out. Thus, under the head of Umbilicaria erosa, Web. (p. 158), he remarks, " In all our British specimens the reaction is medulla K — G red ; but in Fellm. 92, and specimens from Dr. Nyiander and Dr. T. M. Fries, the reaction is medulla K yellow C — ." A similar irregularity is noted under Parmelia conspersa, Ehrh. (p. 135) : " Weddell, in Lich. Prom. Publ., says that in P. conspersa the medulla, when moistened with K, becomes yellow, but almost immediately afterwards becomes red. This I am able to confirm fully, so far as regards foreign specimens ; but on British specimens the yellow reaction takes place, but not always the red." These are mere illustrations of what constantly happens throughout the whole family of Lichens ! Li truth, the reaction-test, introduced by Ny- iander and adopted by Leighton, is so little to be trusted, that its results vary, not only in the hands of different experimenters manipulating the same species, but in those of the same observer, operating on the same specimen at difierent dates ! Still more, then, is variation in result to be looked for in different specimens of the same genus, gathered under dif- ferent circumstances of soil and climate. At present there seems no limit to the differentiation of Lichen-genera and species, and the necessarily involved multiplication of names, by the adoption of new " characters " that are trivial because they are inconstant. Classification is based on no single, uniform, or intelligible principle. Differentiation is determined sometimes by one character, sometimes by another, — the determining characters differing extremely in value, if sometimes they possess any value at all ! Small genera are divided, while large ones are left intact, though the characters of the species of the latter are infinitely more varied than those of the former. In short, the whole system of arrangement is eminently arbitrary and artificial, complex and confusing. In Leighton's Lichen-flora, for instance, while there is only one species of Usnea, there
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