NATURAL ORDERS. 149 



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 num- 

 bers of the Natural Orders of plants contained in the her- 

 barium 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 natu- 

 ralist with less hesitation, as he has expressed himself dis- 

 satisfied with the materials from which his equinoctial 

 proportions are deduced. Whatever may be the compara- 

 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, Begoniaceee, Laurinse im 

 (Cassytha excepted,) Passiflorese, Myrsinese, Magnohacese, 

 Guttiferse, Hesperideae, Cedrelese, and MeHacese. 



Cycadecs, although not found in equinoctial Africa, exist 

 at the Cape of Good Hope and in Madagascar. 



Piperacea, as has been already remarked by Baron 

 Humboldt,^ are very rare in equinoctial Africa ; and indeed 



' Nov. Gen. et Sp. PI. Orb. Nov. 1, p. 60. 



