344 NEW PUBLICATIONS.
useful Cladonia, — its structure, reprotl action, chemical constituents, utility to man and the lower animals, the role it plays in the grand economy of nature in northern countries, its distribution and variation-forms under diversities of soil and climate, altitude and latitude, — would acquire a more valuable knowledge of Lichens than if he merely possessed an herba- rium containing authentically-named specimens of all the species desciubed in Leighton's ' Lichen-flora,' or even if he had himself collected them, and got them ticketed by Leighton or Nylander.
The latest-published work on British Lichens, that of Leighton, is not, as it might and perhaps should have been, in all respects the best. Thus, it is inferior to the ' English Botany ' in so far as (1) the former contains no plates; (2) the latter gives general descriptions as well as specific diagnoses ; while (3) the older work has the advantage, also, of greater simplicity of ar- rangement, there being only 41 genera and 439 species instead of 73 and 781. So long as there is no work giving, in addition to full descriptions of species, plates illustrative of the external characters as well as internal structure of all British Lichens, the ' English Botany ' must continue a standard — if not, in a sense, the standartl — work on British Lichens, to which all other British Lichen-floras should bear more direct and distinct reference than at present they do. It seems to us extremely desirable, for instance, that all British Lichen-floras should, until the ' English Botany ' is superseded by a modern work of the same type, — a fully-illustrated ' Lichenographia Britannica,' — give the modern synonyms of all its genera and species. Certain genera have been abolished by the use of the micro- scope, which has shown us that they consist merely of sterile conditions of species of other genera, or that they really belong to the category of Alyrie or Fungi. Such are the pseudo-genera Lepraria, Spiloma, Variolaria, and Isldinm. But these obsolete genera are so common, that it is much more important for the student to know what they really are — to what species to refer them — than to become acquainted with the mere names of hosts of new or rare species, which are, in every sense, comparatively un- important ! And yet there is no special exposition of these old and once- important genera in Leighton's ' Lichen-flora,' though doubtless some of them are named, or otherwise referred to, under such heads as Pertu- saria. A satisfactory description of the obsolete genera and species of the ' English Botany ' would form a most useful and attractive essay on certain highly interesting features of the natural history of British Lichens, — including, as it would, an account of (1) the secondary reproductive organs ; (2) various forms of hypertro])hy, or degeneration, or arrested development, of the vegetative system ; (3) various forms and causes of sterility ; (4) the border-land between Lichens on the one hand, and Alyee and Fungi on the other. And this kind of information, again, would be infinitely more important to the student, who is more than a collector and labeller, than any list, with specific diagnoses, of species, and especially of new and rare ones !
Leighton's ' Lichen-flora ' is inferior to Crombie's ' Enumeratio ' in that the latter possesses an index of species, though ic is neither quite correct nor quite comj^lete ; while Mudd's ' Manual ' is superior in that it gives fi^e plates of coloured drawings of sporidia, an index of species and varieties, an introduction descriptive of the general structure and morpho- logy of Lichens, measurements of the sporidia, frequent descriptions of the spermogones based upon personal observation, critical and general