See Mr.Atwater's "Account of the Prairies" in "Silliman's North American Journal" volume 1 page 117.) 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 plants not occurring in the neighbourhood, 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." (6/8.

Azara's "Voyage" volume 1 page 373.) Does this not partly explain the circumstance?
We thus have lines of richly manured land serving as channels of communication across wide districts.
(PLATE 26.

GIANT THISTLE OF PAMPAS.) (PLATE 27.