224 Linnean Society. [May 3, 



valid, Galactia, Vigna, Erythrina ? (perhaps introduced), Rhynchosia, 

 Machcerium. These hsts are sufficient to show how materially the 

 Argentine Flora differs from that of Europe ; but what chiefly con- 

 tributes to give it at first sight a European character is the great 

 number and extraordinary prevalence of naturalized European plants, 

 which have spread so rapidly as to cover the soil to a great extent, 

 and actually to predominate over the native growth. The fallow 

 fields about Buenos Ayres are blue with Echium violaceum ; the 

 banks are covered with the common Fennel ; the ditch-sides and 

 waste grounds are overrun with Chenopodium album, Sonchus olera- 

 ceus and Xanthium spinosum ; Trifolium repens and Medicago denti- 

 culata form much of the herbage near the river-side ; and among 

 the most common grasses are Lolium perenne, L. multiflorum, Hor- 

 deum murinum and H. pratense. And these intrusive strangers are 

 not confined to the cultivated lands or to the neighbourhood of the 

 city; the "thistles" and "clover," which clothe the Pampas of 

 Buenos Ayres for leagues and leagues together, are Carduus Ma- 

 rianus, Cynara Cardunculus and Medicago denticulata, all of Euro- 

 pean origin. It is, as Mr. Darwin remarks, a parallel case to that 

 of the horse and ox, which have, within the last three centuries, 

 spread themselves in such countless numbers over the same 

 countries. Mr. Bunbury regards this wide diflfusion of natu- 

 ralized plants as adverse to the views of those who consider the 

 natural distribution of species as determined solely by favourable 

 local circumstances ; the circumstances in the present instance 

 being evidently highly favourable to the plants in question, which 

 however did not exist in these countries until introduced by the 

 indirect agency of man. 



The social character, so eminently conspicuous in many of the 

 naturalized plants, is observable also, though in a less degree, in 

 several of the indigenous plants of the Pampas of Buenos Ayres, the 

 most remarkable cases observed being Verbena erinoides, V. chamce- 

 dryfolia, Mitracarpum Sellovianum, and a dwarf Solanum, besides a 

 few grasses. This social growth of some particular plants, and the 

 consequent uniformity of vegetation, has, Mr. Bunbury thinks, been 

 before noticed as characteristic of extensive plains. Tropical forms 

 of vegetation occur chiefly on the banks and islands of the principal 

 rivers. They are principally woody climbers, such as Passiflora 

 carulea, Stigmaphyllum littorale, two or three species of Paullinia, a 

 Cardiospermum and a Bignonia ; or Leguminosce of a tropical cha- 

 racter, species of Mimosa, Inga, Calliandi-a and Cassia. One solitary 

 species of Melastomacece (an Arthrostemma) reaches to the north 



