Filices. eae 
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 mumber 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- 
Fig. 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 lerns (fig. 261) may be 
