Trib, L PARMELIACEL 



Apothecia rounded and open, or more rarely subglobose 

 and persistently more or less closed ; a thalline exciple mar- 

 gining a normally discoid hyineniuni which rests on a mostly 

 imperfect proper exciple (hypothecium). 



In this vast tribe, perhaps the first to attract the attention 

 of lovers of nature, and to be studied, it is the thallus which 

 plays the chief part ; and this, by its endless variations, lends 

 interest to our latest studies. The predominance of the thallus 

 is seen equally in the fruit. Except in the lowest groups, the 

 proper exciple is for the most part reduced here to a layer of 

 cells supporting the hymenium ; while, on the other hand, a 

 thalliue receptacle, of but subordinate value when found in other 

 tribes, is here characteristical. And it is, once more, the thallus, 

 which fitly determines the families, or largest groups, into which 

 the tribe breaks up. 



It requires little consideration to discern that Usnea is an 

 extreme, as well of Parmeliacei as of Lichenes ; and the group 

 of genera which associate themselves with it, will constitute our 

 first family USNEEI. But the variations of Usneei bring it into 

 closest relations with Parmelia and its allies ; and we find thus 

 our second family PARMELIEI. Close to Parmelia, and yet dif- 

 ferenced remarkably by their texture, manner of attachment, and 

 abnormal fruit, follow the UMBILICAKIEI. And close to the last 

 succeeds tropical Sticta, represented at the north by only a few 

 species; and its associates PELTIGEREI. With this family 

 begins a modification (already spoken of) of the structure of the 

 thallus; a change, that is to say, in the constitution of the 

 gonimous or green layer ; this being constituted, in one group of 

 species of Sticta, Nephroma, Peltigera, and Solorina, of the ordi- 

 nary gonidia, and, in another, not otherwise separable, of the 

 very distinct, and gelatinous gonimia. This structural modifica- 

 tion, which, owing to the darker colour of the gonimia, affects 

 more or less the external coloration of the lichens conditioned 

 by it, and becomes thus, to a considerable degree, discoverable 

 by the naked eye, recurs again in our next succeeding family 

 of mostly humble forms, the humblest indeed we have yet 

 reached PANNAKIEI. And it reaches its height, and the gela- 

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