27 



CLASSIFICATION. 



Before proceeding with the enumeration of species, it 

 will much facilitate the process if we will take a little 

 trouble to understand what are the prominent features 

 of the groups, called genera, under which the species are 

 classed. The enumeration of these characters here will 

 also prevent the necessity of recurring to them hereafter, 

 and, being brought together in one chapter, rendered 

 more easy of comparison when it is desired to determine 

 to what genus any unknown specimen may belong. 



The ferns which we shall have to describe may in the 

 first instance be divided into two prim^ary groups, each 

 containing several genera. The distinguishing feature in 

 this separation will be that in one group the tliecce, or 

 spore-cases, are not surrounded by any annidus or ring, 

 which is much the smallest group, and includes but three 

 genera, and which may be named exannulate, or "without 

 a ring." The other and larger group has spore-cases 

 always surrounded or girt by a ring, and this we shall 

 call annulate, or " with a ring." 



First of all, we will examine the small group which we 

 have called 



ExAKNULATE (ivitJiouf a ring). 



As already observed, only three genera constitute this 

 group, of which two have the spore-cases borne on a spe- 

 cial frond, and in the other the spore-cases are borne on 

 the changed upper portion of an otherwise barren frond. 

 In this group it will be observed that the tJiecc;d or spore - 

 cases are not borne in clusters on the backs or margins 

 of unaltered, or but little altered, fronds, but are confined 

 to a special portion of the plant, in which the whole sur- 

 face so set apart is devoted to its spore-bearing office. 

 The spore-cases are themselves globose, splitting across 

 the centre into two valves, to permit the spores to escape. 



