Filices. 



543 



species. Sir W. J. Hooker, in his Synopsis of all Known Ferns, 

 reduces the number of genera to 75, containing about 2,500 

 species; but other authors, who are content to establish genera 

 upon much more slender characters, raise the number to above 

 200. with a corresponding increase in the number of species. 

 It is a fact beyond controversy that Ferns are equally as vari- 

 able as any other class of plants, and this tendency to varia- 



Plg. 261 . Tree Fern. 



tion is well exemplified in our native species, without including 

 the numerous pretty though abnormal forms which have in- 

 creased so vastly in cultivation during the last twenty years. 

 With the exception of a few species from Northern Asia and 

 North America, and perhaps a few from the southern hemi- 

 sphere, we are limited to our native species for hardy subjects 

 in this beautiful group of plants. In sheltered and partially 

 shaded situations, many of the Tree Ferns (fig. 261) may be 



