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Most of the perplexity in the nomenclature of the species of Parmeliopsis 

 has arisen through the confusion of the isidiose plant "B," with the sorediate 

 plant "C" and through the confusion of the names aleurites and diffusa. It 

 will, therefore, be convenient to discuss the two together. In trying to clear 

 up the confusion, it is necessary to keep in mind that species "B" is isidiose 

 above and pale beneath, while species "C" is sorediate above and dark brown 

 to black beneath. The confusion between the two seems to have originated 

 with Acharius himself in the use of the word "farinosus" (mealy) in his original 

 description of Lichen aleurites (Lichenographiae Prodromus, p. 117) and his 

 subsequent use of the word "pulverulentus" (powdery) in the description of 

 Parmelia aleurites in the Synopsis Lichenum (page 208), these terms evidently 

 applying to plant "C." But in both descriptions the plant is said to be "subtus 

 cinerascens" (ashy beneath), which could apply only to plant "B." Nothing 

 is said in Acharius' descriptions about isidia, although he uses the term "coral- 

 loideus" in describing the comparable isidiose species, Parmelia rudecta. When 

 we turn to the plates cited by Acharius, we find the same confusion existing. 

 The figures in Hoffmann's Enumeratio Lichenum {PL 10, fig. 2. 1784.) and in 

 Dickson's Fasciculus Plantarum Cryptogamicarum Brittaniae {Fasc. j, t. 0, 

 fig. 6. 1793.) are too poor to show which plant is intended. In Hoffmann's 

 Plantae Lichenosae (2". 65, fig. 2. 1801.) the figure represents what is here re- 

 ferred to as plant "A," while the text describes our plant "C." In the English 

 Botany {T. 838. 1801.) the figure represents clearly an isidiose plant, but the 

 text describes a sorediate plant. 



The question could be settled only by examining the Acharian types. This 

 the writer has done. The type of Lichen aleurites consists of six specimens 

 mounted together on one sheet. Five of the specimens (four from Sweden and 

 one from Germany) are all alike and are the radiate, densely isidiose plant, " B "! 

 The sixth specimen is the stramineous, sorediate plant "D," and as Acharius 

 invariably refers to his species as cinereous, the presence of this plant on the 

 sheet must have been a slip. There can be no doubt, then, that the name aleu- 

 rites Ach. should be used for the isidiose plant, "B." 



In the application of the name diffusus Weber, it would seem as if there 

 could be little doubt, although the synonymy cited below would indicate that 

 there has been plenty of confusion. Weber's original description (Spicil. Flor. 

 Goett., p. 250. 1778.) is unusually full and states: "In centro pulverulentus 

 est . . color superne ex glauco albescens, inferne ater.'' This certainly can 

 not apply to a plant that is isidiose above and whitish to ashy beneath. Neither 

 can it be applied, as Theodore Fries has done (in Lichenes Arctoi, p. 60, and in 

 Lichenographia Scandinavica, p. 131) to a plant that he describes as "totus. 

 ochroleucus." The name diffusus Web. must be used for the gray sorediate 

 plant with dark under side that is here discussed as "C." 



Nylander in addition to misapplying the name aleurites to the sorediate 

 plant, has applied the name placorodia Ach. to the isidiose plant. Acharius' 

 original description (Synopsis Lichenum, p. 196. 18 14.) applies exactly to the 

 species here called "A," and does not mention isidia or soredia. The type- 



