102 BOTANY OF CONGO. 



Holland, I first suggested the inquiry respecting the pro- 

 portions of the primary divisions of plants as connected 

 with climate ; and I then ventured to state that " from the 

 equator to 30° lat. in the northern hemisphere at least, 

 the species of Dicotyledonous plants are to the Monocoty- 

 ledonous as about 5 to 1, in some cases considerably 

 exceeding, and in a very fev? falhng somewhat short 

 of this proportion, and that in the higher latitudes a 

 gradual diminution of Dicotyledones takes place until in 

 about 60° N., and 55° S. lat. they scarcely equal half their 

 intratropical proportion."^ 



Since the publication of the Essay from which this quota- 

 tion is taken, the illustrious traveller Baron Humboldt, to 

 whom every part of botany, and especially botanical 

 geography, is so greatly indebted, has prosecuted this sub- 

 ject further, by extending the inquiry to the natural orders 

 of plants ; and in the valuable dissertation prefixed to his 

 great botanical work,^ has adopted the same equinoctial 

 proportion of Monocotyledones to Dicotyledones as that 

 423] given in the Paper above quoted ; a ratio which seems to 

 be confirmed by his own extensive herbarium. 



I had remarked, however, in the Essay referred to, that 

 the relative number of these two primary divisions in the 

 equinoctial parts of New Holland appeared to differ con- 

 siderably from those which I had regarded as general within 

 the tropics ; Dicotyledones being to Monocotyledones only as 

 4 to 1. But this proportion of New Holland very nearly 

 agrees with that of the Congo and Sierra Leone collections. 

 And from an examination of the materials composing Dr. 

 Roxburgh's unpublished Elora Indica, which I had formerly 

 judged of merely by the index of genera and species, I am 

 inclined to think that nearly the same proportion exists on 

 the shores of India. 



Though this may be the general proportion of the coasts, 

 and in tracts of but little varied surface within the tropics, 



' Flinders' Voyage to Terra Amlralis, i, p. 5oS. (^Aiile, p. 8.) 



' Nova Genera et Species Planlaniri), quas in perigrinatione orbis novi 



collt'geiuut., &c. Amat. Boi/pluiid el, Alex, de IhimbohU. ex. sclied. aiito<;r. in 



Old. dig. C. S. Kunth, ]815, Varisiis. 



