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 N ATI' UAL (JllDKHS. 1 lO

Holland, according to my own ol)sorvations, and which is probably not very difi'erent from their j)ropoi'tin in India.

In concluding here the subject of the proportional num- bers of the Natural Orders of plants contained in the her- barium from Congo, I nuiy 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 natu- ralist with less hesitation, as he has expressed himself dis- satisfied "with the materials from ^vhich his equinoctial proportions are deduced. AVhatever may be the compai'a- tive 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 circumstances besides merely the degrees of latitude and even the mean temperature must be taken into account in determining their relative numbers. To arrive at satisfac- tory conclusions in such cases, it is necessary to begin by ascertaining 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.

These are Cycadese, Piperacese, Begoniacese, LauriutT :»ci (Cassytha excepted,) Passifloreae, IMyrsincce, jMagnoliacea*, Guttiferce, Hesperidea), Cedrelea), and ^Meliacea?.

Cjjcadece, although not found in equinoctial Africa, exist at the Cape of Good Hope and in jMadagascar.

Pipcracece, as has been already rcmarkiul by Haron Hund:)oldt,^ are very rare in equinoctial Africa ; and iiidceJ

1 Nov. CciK ct Sp. PL Orh. Xov. 1, ;;. GO.

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