584 
APPENDIX. [. Botany of Terra Australis. 
fifth volume of Willdenow’s edition of the Species Plantarum. In their 
geographical distribution Ferns differ from all the other orders of crypto- 
' gamous plants, their maximum being in the lower latitudes, probably near, 
or very little beyond the tropics. Thus Norfolk Island, situated in 29° S. 
lat. and only a few leagues in circumference, produces as many species of 
the order as are described in Dr. Smith’s Flora Britannica- 
But as shade and moisture are essential conditions to the vegetation of 
the greater part of Ferns, few species only have been observed in those 
parts of equinoctial New Holland, hitherto examined. The number of 
species already found, however, in the different regions of Terra Aus- 
tralis exceeds 100, of which, nearly one-fourth are also natives of other 
countries. 
Among the Australian Ferns there is no genus absolutely confined to 
that country, except Platyzoma, but this, perhaps, ought not to be sepa- 
rated from Gleichenia. 
Only two arborescent Ferns have been observed in Terra Australis, 
one in the colony of Port Jackson, the second, Dicksonia antarctica, is 
frequent in Van Diemen’s Island, at the southern extremity of which its 
trunk is not unfrequently from 12 to 16 feet in height. An arborescent 
species of the same genus was found by Forster, in New Zealand, at Dusky 
Bay, in nearly 46° S the highest latitude in which tree ferns have yet been 
observed. It is remarkable that, although they have so considerable a range 
in the southern hemisphere, no tree fern has been found beyond the 
northern tropic : a distribution in the two hemispheres somewhat similar 
to this has been already noticed respecting the Orchidea3 that are parasi- 
tical on trees. 
I have formerly, in treating of the New Holland Asplenia, observed 
that Ccenopteris does not differ from them in the relation its involucra have 
to the axis of the frond or pinna, but merely in having the ultimate pinna 
more deeply divided with one, or, at most, two involucra on each segment, 
towards the margins of which they must necessarily open : hence, the cha- 
racters of both genera not unfrequently occur in the same frond, and are 
even exhibited by the same involucrum when it happens to extend below 
the origin of the segment. 
I have observed also, in the same place, that in Asplenium when the 
