| Zusammenfassung: | 1. The region described includes the savannahs of the Rio Branco and Rupununi Rivers, of Brazil and British Guiana, and the Pakaraima mountains, between these and Mount Roraima in Venezuela. 2. The Rio Branco-Rupununi plains are covered with climatic savannah vegetation. 3. This vegetation is dominated by a Trachypogon plumosus-Curatella americana association, varied by fringing forest along the streams, by bush islands (on higher areas) and by groves of aeta palms (Mauritia flexuosa) in the depressions, in some of which are sedge flats inundated for considerable periods. 4. The upland savannahs of the Pakaraima mountains, from 1000 to 6500 ft., are clothed in more varied vegetation, with Trachypogon plumosus generally dominant, but Paspalum contractum a close second. 5. All this savannah vegetation seems to correspond to a fire climax. 6. The influence of introduced grazing animals, chiefly cattle and horses, has so far been almost negligible on the Rupununi grasslands, comparatively slight on the Rio Branco savannahs, and non-existent on the upland meadows. 7. Trachypogon plumosus is readily eaten by cattle, especially its fresh growth. Other plants eaten are Byrsonima verbascifolia, Paspalum anceps, Sporobolus cubensis and Paspalum lachneum. 8. Birds, by dropping seeds of forest plants from the branches of savannah trees, and mound-building ants and termites, by offering optimum growing conditions to forest fringe plants, may be concerned on all these types of savannahs, in the initiation of bush islands. 9. The forests of the Pakaraima mountains, from the savannah foothills to 4000 ft. on Mt Roraima, may be divided into seven main types, one of deciduous woods, two of mixed rain forest and four of rain forest consociations each dominated exclusively by one tree species. 10. Notes additional to those of Martyn are appended on the Berbice savannahs, which show a great general similarity to those of the Rupununi, with a few notable physical and vegetational differences.
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