INTRODUCTION TO CKYPTOGAMIC BOTANY. 411 



is, perhaps, as patient of cold as any Lichen occurring in the 

 extreme points of vegetation, both in the arctic and antarctic 

 regions, and by no means confined to them. The black-fruited 

 CladonicB belong to the Australian regions, and this genus, 

 whose species on the whole are remarkably cosmopolitan, has 

 a few very fine endemic species within the American tropics. 

 Spermatogonia have been described by Tulasne in most of the 

 genera. 



8. Parmeliacei, Fr. 



Disc orbicular, or reniform, persistent (not deUquescent) ; 

 bordered by the thallus. 



447. The highest forms of which, apparently, Lichens are 

 capable, are contained in this division ; which, like most of 

 the more typical groups, abo\mds in species. The hymenium 

 is here surrounded by the edge of the thallus, without any 

 proper excipulum. The tribe contains three very distinct 

 groups, separated from each other by general habit and by 

 technical characters ; a large portion of our more widely dif- 

 fused Lichens, whether growing on the ground, attached to 

 rocks or trees, belong to it, and it contains many of the more 

 useful productions of the order. Some of them abound to 

 such a degree as to mask almost completely the trees on which 

 they grow ; others form patches a foot, or even many feet, wide,* 

 on rocks; while localities almost constantly moist with salt 

 spray are not exempt. It is amongst these that we find the 

 more valuable species. In two of the groups the thallus is 

 horizontal, and often foliaceous ; in the third it is vertical and 

 frequently branched. 



a. Peltigeri, Mont. 



Apothecia at first veiled. ThaUus horizontal 



* Some of the large patches of Parmdia, which occur on rocks, are 

 of very great age. Patches of such Lichens as Lecidea geographica 

 probably date from almost fabulous periods, and even small patches are 

 often of considerable age. I have myself watched individuals for 

 twenty-five years, which are now much in the same condition as they 

 were when they first attracted my notice. Plants which endure with- 

 out injury such extremes of temperature and conditions of the Hygro- 

 meter, would seem, d priori, to be likely to have great powers of lon- 

 gevity. 



