148 BOTANY OF CONGO.
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 pub- lished by M. du Petit Thouars," and the still more complete riora of that Island, for which I am indebted to Captain Dugald Carmichael, they are to the Phsenogamous plants as two to three.
The equinoctial proportion of Ferns in level and open tracts, is extremely different 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 Phsenogamous plants, not more than three species of Ferns were found, and those very sparingly. In Egypt it appear, both by Forskal's catalogue and the more extensive Flora of M. Delile, that only one Fern^ has been observed.
463] In Russel's catalogue of the plants of Aleppo two only are noticed : and even in M. Desfontaines' Flora Atlantica not more than eighteen species occur, or with relation to the Phgenogamous plants, about one to one hundred.
The Ferns in the herbarium from Congo, are to the Phsenogamous plants as about one to twenty-six, which agrees nearly with their proportion in Forskal's catalogue of the plants of Arabia, with that of the north coast of New
1 Beatsons Tracts relative to St. Hele^ia, p. 295. - Melanges de Bota?iique.
^ ]Si"amed Adiantnm capillKS veneris by both these aut.liors; but possibly a nearly related species that has often been confounded with it. Of the species I allude to, which may be called Adiantnm Africannm, I have collected speci- nieus in Madeira, and have seen others from Teneriffe, St. Jago, Mauritius or ]sle de Bourbon, aud Abyssinia. Adiantum Africannm has also been confounded with A. tenerum of Jamaica, and other West India islands, and the latter with A. capilhis veneris, which has in consequence been supposed common to both hemispheres, to the old and new continent, aud to the torrid and temperate zones.
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