��The following statistics, compiled from the works quoted, will serve to show both the general mimerical richness of the British Lichen-flora at different dates, according to diflerent authors ; and tlie rate of progress in the addition of so-called neio species, during the last thirty years.
1. 'English Botany,' 2nd ed. 1844. Number of genera, 41. Number of species, 439.
Average number of species in each genus 10-70
2. Mudd, 'Manual,' 1861. Number of genera, 105. Number of species, 497.
Average number of species in each genus, 4-73.
3. Crombie, ' Lichenes Britaunici,' 1870. Number of genera, 72.
Number of species, 658.
Average number of species in each genus, 9-14.
4. Leighton, 'Lichen-flora,' 1871. Number of genera, 73. Number of species, 781.
Average number of species in each genus, 10-69. !
If progress in knowledge is to be measured by the number of species added withni a given period to a national Lichen-flora, it must be ad- mitted that the progress of British Lichenology has been very great since 1 844, inasmuch as the number of British Lichens has been, during these twenty-seven years, nearly doubled— the actual numbers being 781 against 439. Such a criterion of progress is, however, utterly fallacious." The first effect of such large additions, in the form of new' species, is simply to bewilder the student, and render the existing confusion of classification "worse confounded." It seems to us infinitely more important to arrange in a simple, intelligible way, that will attract students, existino- niaterials, than incessantly and inordinately to hunt after " new and rare'" species, as is the fashion of the majority of our Lichenologists. But in saying so, we do not deny that collectors and collections have a recoo-. iiized value, and that they are indispensable to the progress of Licheno- logical science. In the hands of the philosophic botanist new species will be relegated to their proper rank in classification, and they will be made to illustrate variations of form, peculiarities of local or general dis- tribution, affinities of geographical floras, as well as many phenomena of the highest interest in the physiology, organology, and 'classification of Lichens. But, notwithstanding that, during the last thirty years, we have learned much concerning the minute anatomy of Lichen's, and espe- cially their reproductive organs ; as well as concerning their chemical con- stituents and^ their economical applications, such a work as Leighton's ' Lichen-flora ' really gives, comparatively, less information concerning the general natural history of British Lichens than did the good old ' English Botany,' which is so apt now-a-days to be set aside by the microsc'ope- proud nomenclator.
The character of many, at least, of the "new species" recorded in Leighton's ' Lichen-flora ' may be gathered from the following illustra- tions. Of Ferrucaria polysiicta, Borr. (p. 422), we are told " This and/«5- cella may be only states of the same Lichen." Then why separate them until they are proved, by sufficient characters, to be distinct,' and each to require