218 CHAEACTEES OF TEIBES AND GENEEA. 



belonging to this genus ; they have a wide geographical 

 range; extending from the arctic to the antarctic circles, 

 and abounding in the tropics, ascending to great elevations. 

 Its most common representatives are forms analagous to 

 the Polypodium aculeatum, Linn. (Aspidium, SwS), of the 

 Eupropean flora, of which there are several states found in 

 our own country sufficiently distinct to be considered 

 separate species by some botanists, though others view 

 them as only different states of one variable species. A 

 similar difference of opinion exists regarding the foreign 

 forms, the original discoverers having named and described 

 plants from different localities as distinct species, and, 

 indeed, in many instances they seem sufficiently distinct 

 to be readily acknowledged as such, but on collating a 

 general collection of specimens and regarding them from a 

 Darwinian point of view, it is difficult to consider the great 

 majority of them otherwise than as climatic conditions of a 

 single species ; and the same may be said of the group 

 represented by P. coriaceum. The difference in some of the 

 extreme forms is, however, so obvious, especially when 

 living examples are examined, that it seems reasonable to 

 distinguish them by different names, and I therefore, after 

 much consideration, think it best to enumerate them under 

 the original names given by authors. 



As a genus, Polystichum is technically distinguished 

 from Lastrea by its indusium being circular and peltate, 

 instead of reniform, as in the latter. This character, 

 however, cannot be invariably depended upon, for in some 

 species with the habit of Polystichum have reniform in- 

 dusium, and instances occur where peltate and reniform 

 indusia are found on the same frond. To determine the 

 genus, it is therefore necessary to study its habit. As a 

 general rule, Polystichum may be known from Lastrea by 



