A voluminous _History of Plants_ had been published in 1751 by Sir John Hill[63], the first superintendent to be appointed to the Royal Gardens, Kew. In the _History_ lichens are included under the Class “Mosses,” and are divided into several vaguely limited “genera”—_Usnea_, tree mosses, consisting of filaments only; _Platysma_, flat branched tree mosses, such as lung-wort; _Cladonia_, the orchil and coralline mosses, such as _Cladonia furcata_; _Pyxidium_, the cup-mosses; and _Placodium_, the crustaceous, friable or gelatinous forms. A number of plants are somewhat obscurely described under each genus. Not only were these new _Lichen_ genera suggested by him, but among his plants are such binomials as _Usnea compressa_, _Platysma corniculatum_, _Cladonia furcata_ and _Cladonia tophacea_; other lichens are trinomial or are indicated, in the way then customary, by a whole sentence. Hill’s studies embraced a wide variety of subjects; he had flashes of insight, but not enough concentration to make an effective application of his ideas. In his _Flora Britannica_[64], which was compiled after the publication of Linnaeus’s _Species Plantarum_, he abandoned his own arrangement in favour of the one introduced by Linnaeus and accepted again the single genus _Lichen_.
Sir William Watson[65], a London apothecary and physician of scientific repute at this period, proposed a rearrangement and some alteration of Linnaeus’s sections. He had failed to grasp the principle of development, but he gives a good general account of the various groups. Watson was the progenitor of those who decry the makers and multipliers of species. So in regard to Micheli, who had increased the number to “298,” he writes: “it is to be regretted, that so indefatigable an author, one whose genius particularly led him to scrutinize the minuter subjects of the science, should have been so solicitous to increase the number of species under all his genera: an error this, which tends to great confusion and embarrassment, and must retard the progress and real improvement of the botanic science.” Linnaeus however in redressing the balance earned his full approbation: “He has so far retrenched the genus (_Lichen_) that in his general enumeration of plants he recounts only 80 species belonging to it.”