NATURAL OKIJEKS. 143
In other intratropical countries tlic proportion may be still smaller ; but I can neither adopt the general equinoctial im ratio given by Baron Humboldt, namely, that of 1 : 00, nor suppose with him that the minimum of the order is within the tropics. For Cyperaceae, like Rubiaceae, and indeed several other families, is composed of tribes or ex- tensive genera, having very diflerent relations to climate. The mass of its equinoctial portion being formed of Cyperus and Fimbristylis, genera very sparingly found Ijeyond the torrid zone ; while that of the frigid and part of the tempe- rate zones consists of the still more extensive genus Carex, which hardly exists within the tropics, unless at great heights. Hence a few degrees beyond the northern tropic, on the old continent at least, the proportion of Cyperaceae is evidently diminished, as in Egypt, according to ^I. Delile's valuable catalogue ;^ and the minimum will, I be- lieve, be found in the Flora Atlantica of M. Desfontaines and in Dr. Russel's catalogue of the plants of Aleppo." It is not certain, however, that the smallest American pro- portion of the order exists in the same latitude. And it appears that in the corresponding parallel of the southern hemisphere, at the Ca])e of Good Hope and Port Jackson, the proportion is considerably increased by the addition of genera either entirely different from, or there more extensive than, those of other countries.
Among the Cyperaceae of the Congo herbarium there are fifteen species of Cyperus, of which C. Fapjiii's appears to be one. The abundance of this remarkable species, especially near the mouth of the river, is repeatedly noticed in Professor Smith's journal, but from the single specimen with fructificalion in the collection, its identity with the plant of Egypt and Sicily, though very probable, cannot be absolutely determined. I perceive a very slight ditfereucc in the sheaths of the radii of the common umbel, Avhich in the plant from Congo are less angular and less exactly truncated, than in that of Egypt ; in other respects the two plants seem to agree. I have not seen C. laxifiorus, a
^ Flor. ^Egi/pt. Illustr. in Descrip. de VEgypte, Uist. Xat. 2, p. 49. ' Nat. Hist, of Aleppo, 2/id ed. vol. 2, 7;. 242,
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