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 

 llora 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 Carpentaiia, 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. Dehle, that only one 

 Fern' has been observed. 



«3] 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 

 Phasnogamous 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 Beatson's Tracts relative to St. Helena, p. 295. ^ Melanges 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, which may be called Adiantum Africamtm, I have collected speci- 

 mens in Madeira, and have seen others from Teneriffe, St. Jago, Mauritius or 

 Isle de Bourbon, and Abyssinia. Adiantum Africanum has also been confounded 

 with A. tenerum of Jamaica, and other West India islands, and the latter with 

 A, capillus veneris, which has in consequence been supposed common to both 

 hemispheres, to the old and new continent, and to the torrid and temperate 

 zones. 



