152 BAHIA BLANCA TO BUENOS AYRES. 



served in the prairies* of North America, where 

 coarse grass, between five and six feet high, when 

 grazed by cattle, changes into common pasture 

 land. I am not botanist enough to say whether 

 the change here is owing to the introduction of new 

 species, to the altered growth of the same, or to a 

 difference in their proportional numbers. Azara 

 has also observed with astonishment this change : 

 he is likewise much perplexed by the immediate 

 appearance of 2:)lants not occurring in the neigh- 

 bourhood, on the borders of any track that leads to 

 a newly-constructed hovel. In another part he says, 

 " ces chevaux (sauvages) ont la manie de preferer les 

 chemins, et le bord des routes pour deposer leurs 

 excremens, dont on trouve des monceaux dans ces 

 endroits."t Does this not partly explain the cir- 

 cumstance 1 We thus have lines of richly-ma- 

 nured land serving as channels of communication 

 across wide districts. 



Near the Guardia we find the southern limit of 

 two European plants, now become extraordinarily 

 common. The fennel in great profusion covers the 

 ditch-banks in the neighbourhood of Buenos Ayres, 

 Monte Video, and other towns. But the cardoon 

 (Cynara cardunculus)| has a far wider range : it 



* See Mr. Atwater's account of the Prairies, in Silliraan's N. A. 

 Journal, vol. i., p. 117. f Azara's Voyage, vol. i., p. 373. 



t M. A. d'Orbigny (vol. i., p 474) says that the cardoon and 

 artichoke are both found wild. Dr. Hooker (Botanical Magazine, 

 vol. Iv., p. 2862) has described a variety of the Cynara from this 

 [)art of South America under the name of inermis. He states 

 that botanists are now generally agreed that the cardoon and 

 the artichoke are varieties of one plant. I may add, that an in- 

 telligent farmer assured me that he had observed in a deserted 

 garden some artichokes changing into the common cardoon. Dr. 

 Hooker believes that Head's vivid description of the thistle of the 

 Pampas applies to the cardoon ; but this is a mistake. Captain 

 Head referred to the plant, which I have mentioned a few lines 

 lower down, under the title of giant thistle. Whether it is a true 

 thistle, I do not know ; but it is quite different from the cardoon, 

 and more like a thistle properly so called. 



