to systematic order has been receritly made known to the world by Dr. Acharius, a learned Swede, who in his Prodromus, and Methodus Lichenum, has divided it into genera founded on the receptacle of the seeds alone. Hence those genera, though more technical, are less natural than Hoffmann's; but they will, most likely, prove the foundation of all that can in future be done on the subject, and the works of Acharius form a new æra in cryptogamic botany. It is only perhaps to be regretted that he has been somewhat too prodigal of new terms, which when not wanted are always a burthen to science, and rather obscure than illustrate it. Thus Hedwig used the term sporangium for a seed-vessel, pericarpium, in which the learner would seek in vain for any distinction, or new idea. A student might very justly complain if, in a science necessarily so overburthened with words, he were required to call the same part by a different name in every different family. I would gladly therefore retain the word frons in preference to the thallus of Acharius, re-
