462 APPENDIX. No. V. 



inferior, perhaps, to that of equinoctial countpies 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 Phjeno- 

 (Tamous plants is probably about one to twenty, even on continents where the 

 tracts most favourable to theii- production form only a small part, their number 

 beinff 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 pi-oportion to Pha?nogamous 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 al)out 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,f 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. I'erdinand 

 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 Phaenogamous 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 Ibund 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 Phasnogamous 

 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. 



* Melanges de Bol. Observ. add. a M. de Lamarck, p. 6, el 38. 



+ Beahon's Tracts relative to Si. Helena, p. 295. J MUanges de Botanique. 



*) Named Adiantum capiUus veneris by both these authors; but possibly a nearly 



related species that has often been confounded with it. Of the species I allude to, 



