or nearly as on the shores of equinoctial countries. And analogous to this inversion it appears, that at corresponding Alpine heights, both in the temperate and frigid zones, the proportion of Dictyledones is still further increased.
The acotyledonous or cryptogamous plants of the herbarium from Congo, are to the phænogamous as about 1 to 18. Some allowance is here to be made for the season, peculiarly unfavourable, no doubt, for the investigation of this class of plants. But it is not likely that Professor Smith, who had particularly studied most of the cryptogamous tribes, should have neglected them in this expedition; and the circumstance of the very few imperfect specimens of Mosses in the collection being carefully preserved and separately enveloped in paper, seems to prove the attention paid to, and consequently the great rarity of, this order at least; which, however, is not more striking than what I have formerly noticed with respect to some parts of the north coast of New Holland.[1]
I have in the same place considered the Acotyledones of equinoctial New Holland, as probably forming but one thirteenth of the whole number of plants, while the general equinoctial proportion was conjectured to be one sixth. This general ratio, however, is certainly over-rated, though it is probably an approximation to that of countries containing a considerable portion of high land. Within the tropics, therefore, it would seem that the ratio of acotyledonous to phænogamous plants, varies from that of 1:15 to 1:5; the former being considered as an approximation to the proportion of the shores, the latter to that of mountainous countries.
425] II. The NATURAL ORDERS of which the herbarium from Congo consists are 87 in number; besides a very few genera not referable to any families yet established. More than half the species, however, belong to nine orders, namely, to Filices, Gramineæ, Cyperaceæ, Convolvulaceæ, Rubiaceæ, Compositæ, Malvaceæ, Leguminosæ, and Euphorbiaceæ; all of which have their greatest
