APPENDIX. No. V. 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 Phanogamous plants, about one to one hundred. 
The Ferns in the herbarium from Congo, are to the Phaenogamous 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 Holland, 
according to my own observations, and which is probably not very different 
from their proportion in India. 
In concluding here the subject of the proportional numbers of the Natural 
Orders of plants contained in the herbarium from Congo, I may observe, that 
the ratios I have stated, do not always agree with those given in Baron 
Humboldt’s learned dissertation, so often referred to. I have ventured, 
however, to differ from that eminent naturalist with the less hesitation, as he 
has expressed himself dissatisfied with the materials from which his equinoctial 
proportions are deduced. Whatever may be the comparative value of the 
facts on which my own conclusions depend, I certainly do not look upon them 
as completely satisfactory in any case. And it appears to me evident, that 
with respect to several of the more extensive natural orders, other cireum- 
stances besides merely the degrees of latitude and eyen the mean temperature 
must be taken into account in determining their relative numbers. To arrive at 
satisfactory conclusions in such cases, it is necessary to begin by ascertainme 
the geographical distribution of genera, a subject, the careful investigation of 
which may likewise often lead to important improvements in the establishment 
or sub-divisions of these groups themselves, and assist in deciding from what 
regions certain species, now generally diffused, may have originally proceeded. 
To the foregoing observations on the principal Natural Orders of Plants 
from the banks of the Congo, a few remarks may be added on such families 
as are general in equinoctial countries, but which are not contained in the 
collection. 
which may be called Adiantum africanum, I have collected specimens in Madeira, and 
have seen others from Teneriffe, St. Jago, Mauritius or Isle de Bourbon, and Abyssinia. 
Adiantum africanum has also been confounded with 4. tenerum of Jamaica, and other 
West India Islands, and the latter with 4. 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. ; 
