302 GYMNOCAEPEI. PART n. 



are motile, though not provided with cilia, and are sup- 

 posed to be fertilizing particles like pollen, since they do 

 not germinate as spores do. In this vast family of open- 

 shielded lichens, which comprises every form and habit 

 of the plant, the preceding type, which is the highest, 

 undergoes many modifications ; but the essential cha- 

 racter remains the same, and the group is so natural, 

 that the species run into one another so as to leave no 

 very striking distinction. 



Commencing with the GTMNOCAEPEI, the Parmeliacei 

 first claim notice as containing the highest types which 

 lichens are capable of assuming, and as abounding in 

 species. The disc, which is the hymenium, is orbicular or 

 kidney-shaped, and surrounded by the frond, without any 

 proper excipulum or cortical covering. A large portion 

 of our most widely diffused lichens, whether growing 

 on the ground or attached to rocks and trees, belong to 

 this tribe ; they form patches two or three feet in dia- 

 meter, which are often of marvellous antiquity, and they 

 grow so slowly that even small patches are of great age. 

 This tribe consists of three distinct groups : in two of 

 these the plants are horizontal and sometimes foliaceous ; 

 in the third they are vertical, often branched, and oc- 

 casionally pendulous. 



The latter group of this large division of lichens com- 

 prises the genera allied to Usnea, which are erect, 

 centripetal lichens, that is to say, their body or thallus 

 is, an upright and generally cylindrical stem, in the 

 centre of which the layer of marrow, the origin of 

 fructification, is condensed, and the open discs, or 

 hymenia, are in connection with it, whether they be 

 situated at the ends of the branches, or on the surface 

 of the upright stems. The TJsnese have three forms, 

 the pendulous, the inflated and erect, and the branched 

 or shrubby. The Evernia jubata is an example of the 



