416 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



454. The same country, and the south temperate regions 

 generally, are the especial seat of the remarkable genus Sticta. 

 In all Europe, only about twelve Sticta; occur (several of which 

 are almost peculiar to the western coast and Ireland, more 

 especially to our own) ; whereas New Zealand and Chili each 

 contain at least twice that number. In those parts of North 

 America comprised in Tuckermann's enumeration (i.e., all the 

 country north of 40°), we have only eight species, and in 

 French Guiana only two. In other parts of tropical America, 

 however, they are somewhat more abundant. It is remarkable 

 that the Loharia section of this genus (two species of which 

 occur in Europe generally, and which are found also in North 

 America, and of which the tropics have a few pecuhar species) 

 should be almost wholly absent from those regions in which 

 the majority of the species occur. Here, however, again, we 

 perceive how unsafe it would be to affirm its non-existence in 

 the south temperate zone ; for one species, according to Flotow, 

 occurs at the Cape of Good Hope, and in all probability it will 

 be found elsewhere. 



C. USNEACEI, Uschw. 



Disc open from the first ; thallus mostly centripetal, vertical, 

 or sarmentose, without any hypothallus. 



455. The third sub-tribe of this large division comprises 

 the genera allied to Usnea. All the species, with the excep- 

 tion of Cetrariw, have a centripetal thallus, which is usually 

 erect and branched, with a disc open from the earliest stage of 

 growth. They are connected with the Euparmeliacei by means 

 of Cetrarice, which have very nearly the same habit. The 

 thallus, indeed, though not absolutely erect, has an ascending 

 direction in very young individuals, which becomes more and 

 more vertical as it approaches maturity. Indeed, Cetraria 

 tristis has only that degree of inclination wliich arises from its 

 crowded mode of growth, and springs like a seaweed from a 

 little peltate disc. Cetraria jnnastri and Juniperina have 

 the beautiful colours of a Sticta. Roecella (Fig. 18, c) departs 

 from the Parmelioid type, and has the dull grey tints of 

 Ramalina, assuming a fungoid or fucoid aspect. The disc, 

 which is here open from the earliest stage of growth, is seated 



