INTRODUCTION TO CRYPTOGAMIC BOTANY. 417 



on a carbonaceous stratum. The supposed species run very 

 mucli into each other, and may be reduced to a very few. 

 Their peculiar habit alone separates them evidently from 

 Evernia. Ramalina affects occasionally the same marine 

 habitats as Roccella. It is very near to Evernia, with some 

 species of which it is almost confluent. The thallus is, how- 

 ever, more distinctly analogous to that of Clavaria, being 

 always ahke on aE sides, without any distinct hypothallus. It 

 is curious that while R. polymorpha and scopulorum abound 

 in dyeing matter. It. caUcaris is rich in gluten. 



456. This sub-tribe contains three distinct types ; the first 

 distinguished by its pendulous habit ; the second inflated and 

 erect, of which JDufourea madreporiformis and fla'tyimea 

 are well-known examples, the latter of which abounds in the 

 guano islands, on the coast of Africa ; and thirdly, the true 

 Eamalinoid type, with which every one is familiar, from the 

 frequency of the species on wooden structures. Thysanothe- 

 ciwm, Berk, and Mont, a Swan River Lichen, is perhaps only 

 a form of Ramalina, though its characters are very remark- 

 able. The absence of fertile asci makes this the more probable. 

 Evernia exhibits several types, and contains many elegant 

 species. Thus E. vulpina and fiavicans present beautiful 

 tints, while most of the species are rather sombre. E. jubata, 

 again, is remarkable for its pendulous, cylindrical branched 

 thallus, hanging down like bunches of horse-hair from rocks 

 and trees. Usnece, finally, when well-grown, are perhaps the 

 most beautiful of Lichens. The colours are sometimes bril- 

 liant, and the habit elegant, and, when the broad discs are 

 amply ciliated, the appearance is very striking. The same 

 species are widely diSiased, but the colours are brighter in exotic 

 specimens. Usnea melaxantha (Fig. 15, a), with U. Taylori, 

 are splendid productions. 



457. The tribe is mostly cosmopolitan, a remark which applies 

 to species as well as genera. Usnea, Cetraria, and Ever- 

 nia, are as genera ubiquitous, but they contain many local 

 species. In Europe several Cetrarice are almost pecuhar to 

 the Western and Mediterranean coasts. Cetraria dimLuishes 

 greatly under the tropics. Roccella avoids extremes of both 

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