104 BOTANY OF CONGO. 



or nearly as on the shores of equinoctial countries. And 

 analogous to this inversion it appears, that at correspond- 

 ing 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 phsenogamous as about 

 1 to 18. Some allowance is here to be made for the 

 season, pecuharly unfavourable, no doubt, for the investi- 

 gation 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 imper- 

 fect 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.^ 



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 con- 

 taining a considerable portion of high land. Within the 

 tropics, therefore, it would seem that the ratio of acotyle- 

 donous to phsenogamous plants, varies from that of 1 : 1 5 

 to 1 : 5 ; the former being considered as an approximation 

 to the proportion of the shores, the latter to that of moun- 

 tainous countries. 



425] II. The NATURAL ORDERS of which the herba- 

 rium from Congo consists are 87 in number; besides a 

 very few genera not referable to any families yet esta- 

 blished. More than half the species, however, belong to 

 nine orders, namely, to Filices, Graminese, Cyperacese, Con- 

 volvulaceae, Rubiacese, Compositse, Malvaceae, Leguminosse, 

 and Euphorbiacese; all of which have their greatest 

 1 Flinders' Foyaye, 2, j). 539. {Ante, pp. 9, 10.) 



