Linruean Society'. 463 



merly British Minister at Buenos Ayres, and afterwards at Rio de 

 Janeiro) in the neighbourhood of Buenos Ayres, Monte Video, Mal- 

 donado, and other localities on the northern shore of the Rio de la 

 Plata, and along the lower part of the River Uruguay, aided by a 

 residence of about a month at Buenos Ayres in the beginning of 

 1834, during which he had himself the opportunity of becoming 

 acquainted with the most prominent features and general aspect of 

 the vegetation. The principal published works which he has con- 

 sulted are M. Auguste de St. Hilaire's ' Report of his Travels in 

 Southern Brasil' (in the ninth volume of the ' Memoires du Mu- 

 seum d'Histoire Naturelle'), and the papers by Sir Wilham Hooker 

 and Dr. Walker- Arnott " On the Plants of Extratropical South 

 America," in the 'Botanical Miscellany' and 'Journal of Botany;' 

 and he also acknowledges his obligations to Sir William Hooker for 

 very important assistance in naming the specimens contained in 

 Mr. Fox's collections. 



The region of which he proposes to treat is defined as lying on 

 both banks of the Rio de la Plata, and on the lower part of the 

 courses of the two great rivers by whose junction it is formed ; and 

 consequently comprises those parts of the republics of Buenos Ayres 

 and the Banda Oriental which lie nearest to the Plata, between the 

 parallels of .33° and 35° S. lat. The collections were chiefly formed 

 in the neighbourhood of the coasts and of the rivers. Mr. Fox also 

 made large collections in the southernmost part of Brasil ; on the 

 vegetation of which Mr. Bunbury proposes occasionally to remark, 

 as forming a connecting link, botanically as well as geographically, 

 between the Buenos- Ayrean districts and the tropical parts of the 

 same continent. Geologically the Rio de la Plata (which as far up 

 as Buenos Ayres is between twenty and thirty miles wide) forms a 

 strongly marked boundary, separating two widely extended and very 

 dissimilar formations. All its northern shore is composed of cry- 

 stalline rocks (granite and gneiss, and their various modifications), 

 which range from thence to the northward uninterruptedly through 

 many degrees of latitude, constituting the whole coast of Brasil, 

 even it is said as far as Bahia. On the south of the great river 

 nothing is seen but tertiary formations of a very late date ; first, 

 the mud and marl of the Pampas, and further south the gravel and 

 shingle of Patagonia. The line of demarcation between these two 

 formations is absolute ; but notwithstanding this remarkable differ- 

 ence in the structure of its banks, the Plata does not form a botani- 

 cal boundary. There are indeed several species of plants which are 

 confined to one side or the other, and some families (principally 

 tropical) which do not cross it ; yet the leading characteristics of 

 the vegetation, both as to its general physiognomy and its prevailing 

 forms, are the same on both sides. The whole country, therefore, 

 from the frontier of Brasil southward, as far as the Pampas vegeta- 

 tion extends (or to the border of Patagonia), may be considered as 

 one botanical province, which, for the sake of convenience, Mr. 

 Bunbury provisionally calls the Argentine region, from the name of 

 the great river. 



