462 APPENDIX. No. V. 
inferior, perhaps, to that of equinoctial countries of moderate elevation, a humid 
atmosphere and protection from the direct rays of the sun, seem to be requisite 
for their most abundant production. 
When all these conditions co-exist, their equinoctial proportion to Phzeno- 
gamous plants is probably about one to twenty, even on continents where the 
tracts most favourable to their production form only a small part, their number 
being increased according as such tracts constitute a more considerable portion 
of the surface. : 
Hence their maximum appears to exist in the high, and especially the well 
wooded, intratropical islands. Thus in Jamaica, where nearly two hundred 
species of Ferns have been found, their proportion to Phanogamous plants is 
probably about one to ten. In the Isles of France and Bourbon, from the 
facts stated by M. du Petit Thouars,* they appear to be about one to eight. 
In Otaheite, according to Sir Joseph Banks's observations, they are as one 
to four. And in St. Helena, from Dr. Roxburgh’s Catalogue,+ they exceed 
one to two. 
This high proportion extends to the islands considerably beyond the southern 
tropic. Thus in the collection formed by Sir Joseph Banks in New Zealand, 
they are about one to six: in Norfolk Island, from my friend Mr. Ferdinand 
Bauer’s observations, they exceed one to three: and in Tristan Da Cunha, 
both from the Catalogue published by M. du Petit Thouars,} and the still 
more complete Flora of that Island, for which I am indebted to Captain 
Dugald Carmichael, they are to the Phanogamous plants as two to three. 
The equinoctial proportion of Ferns in level and open tracts, is extremely dif- 
ferent from those already given; and it is not improbable that as the maximum 
of this order is equinoctial, so its minimum will also be found either within or a 
few degrees beyond the tropics. Thus in several of the low Islands in the 
Gulf of Carpentaria, having a Flora of upwards of two hundred Phenogamous 
plants, not more than three species of Ferns were found, and those very 
sparingly. In Egypt it appears, both by Forskal’s catalogue and the more 
extensive Flora of M. Delile, that only one Fern § has been observed. 
* Mélanges de Bot. Observ. add. & M. de Lamarck, p. 6, et 38. ‘ 
+ Beatson’s Tracts relative to St. Helena, p. 295. + Mélanges de Botanique. 
§ Named Adiantum capillus veneris by both these authors; but possibly a nearly 
related species that has often been confounded with it. Of the species I allude to, 
