BOTANY OF TERRA AUSTllALIS. 59 



FILTCES.^ Of this order nearly 1000 species arc de- 

 scribed in tlic fiftli volume of Willdenow's edition of the [sat 

 Species Plantaruiii. In their geographical distribution, 

 Eerns dift'er from all the other orders of cryptogamous 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 oidy a few leagues in circum- 

 ference, produces as many species of tlic 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 Hol- 

 land hitherto examined. The number of species already 

 found, however, in the different regions of Terra Austral is 

 exceeds 100, of which nearly one fourth arc also natives 

 of otlier countries. 



Among the Australian Ferns ihere is no genus abso- 

 lutely confined to that country, except Platyzoma, but this, 

 perhaps, ought not to be separated from Gleichenia. 



Only two arborescent Ferns have been observed in Terra 

 Australis, one in the colony of Port Jackson, the second, 

 DicJcsonia autarciica, is frequent in Van Diemen's Island, 

 at the southern extremity of which its trunk is not unfre- 

 quently 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 4G° S. the highest lati- 

 tude in vdiich 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 tlie northern tropic : a distribution in the two 

 hemispheres somewhat similar to this has been already 

 noticed respecting the Orchideas that are parasitical on 

 trees. 



I have formerly, in treating of the New Holland Asplenia, 

 observed that CcBuopteris does not differ from them in the 

 relation its involucra have to the axis of the frond or pimin 

 but merely in having the ultimate pinna more dcc2)ly di- 

 vided, with one, or, at most, two involucra on each segment, 



> I'rodr.jl, Nov. IIoU, 115. 



