﻿346 



MR. G. BENTHAM ON THE MIMOSE^. 



LJectural, but wliich may yet be 



command, must be in a great measure speculati 



deserving of a passing notice. 

 Under this head of representative Mimosese in the two hemispheres we may fairly 



r 



include the following nine : 



America. 



Old World. 



Pentaclethra 



Common in North Brazil 



and Guiana, extending to Central America, and 



Dimorphandr 



PlPTADEXIA. 



very closely, with 



South tropical and subtropical 

 Brazil and Paraguay, and closely connected with 

 a series of tropical Brazilian species. 

 [OSA poLTANcisTRA and M. CERAXONIA. Wost ludics 

 and Central America, and closely connected with 

 several species ranging from Brazil to Mexico. 



Pektaclethra macrophylla. 



Limited range in west 



tropical Africa, without any Old- World connex- 



ions. 



Piptadenia afkicaka. West tropical Africa, extend- 

 ing perhaps across to the lower Zambesi, but with- 

 out any newly allied Old- World species. 



Mimosa namata and M. rubicaulis. East India, the 

 former (so near to the American species that one 

 variety is scarcely distinguishable from M. polyan- 

 ctstra) almost limited to the Peninsula, the other 



with 



Africa 



LEuciENA nrvERsiFouA. Tropicol Mexico, and con- 

 nected with several species from West Tropical 



America. 

 Acacia macracvntha. West tropical America and 

 West Indies, with several closely connected tro- 

 pical American species from the same region, some 



with a wider range. 

 Acacia lacerans. Brazil. 



A distinct species, but 



rather more nearly connected with allied species 



of the same country than is the case with A^ Per- 



villeL 

 Acacia panicttxata and A. riparia. Both with a wide 



range over tropical America, and connected with 



several other species common over a great part of 



the same area. 



Mascarene islands (including Madagascar). 

 Leuc^ka Forsteri, South Pacific islands, from New 

 Caledonia to Tahiti, without any near Old-World 



connexions. 



Acacia Sieberiaka. Western tropical Africa, with a 

 limited range, the nearest Old-World connexions 

 in South Africa, but not nearly so close as the 

 American connexions of A. macracantha. 



Acacia Peryillei. Madagascar. No Old-World species 

 approaching it nearly so closely as the A. lacerans. 



PEST^ATA 



with 



range over tropical Asia, and one, if not both, ex- 

 tending over tropical Africa, connected with two 

 more local species, one from south-east Africa, the 



an 



In studying the above list, the first point which strikes us is the marked American 



character of 



out of the nine pairs of species. They are there 



rounded by 



numerous, flourishing, and widely diffused kindred, whilst in the Old World they 



comparatively 



absolutely, isolated and limited to small 



A hasty con- 



clusion might therefore class them with the identical species of the previous list as old 

 colonists, distinguished only as having acquired their idiosyncrasy by a longer isolation. 



cases. Although 



But a further consideration discloses a marked diff< 



the two 



time and isolation are important elements in the modification of races, yet it requires 



something more to produce a change of specific character. 



Circumstances must have 



occurred to bring natural selection into play. A race which has acquired a prosperous 



stability by having 



settled into a constitution suited to the circumstances m 



which 



it is placed, will, if brought to colonize in a country offering similar conditions, most 

 likely there also preserve its identity for an indefinite period, or become too sugntiy 

 modified to be specifically distinguished. But it is different with a race gradually ex- 

 teoding itself in different directions over bordering regions where physical or social con- 

 ditions are more or less modified. In the former case, notwithstanding the innumerable. 





