Since Darwin's report on the Pampa grassland appeared, various opinions have been presented onthe problem (Grisebach 1872; Hann 1911; Köppen 1900, 1918 etc.). However, until the 1920's, the Pampa problem did not attract great attention in world academic circles. It was Schmieder's (1927) paper which marked the turning point in research on this problem. On the basis of various materials, he concluded that the Pampa is not a natural but a culturally induced grassland. His thesis became a focus of attention and, at the same time, of serious criticism. Kühn (1929), one of the reviewers, refuted the “evidence” referred to by Schmieder point by point, and concluded that the Pampa should be considered a natural grassland. Thereafter, hydroclimatic water balance, vegetation ecology, and regional ecology have been intensively studied, and the Schmieder's thesis has lost the backing of major researchers. Hydroclimatological research has contributed much to research on the Pampa problem. On the basis of intensive research on the relationship between the distribution of hydroclimatic water balance and the representative natural vegetation in the USA, Thornthwaite (1952) hypothesized the presence of a grassland climate. Similar results were obtained by his collaborators on the Pampa. He is of the opinion that the grassland is a natural phenomenon, in equilibrium with its climatic environment, and that it is possible to explain the presence of grassland on the basis of climate alone without bringing in other aspects such as human activities or fire; this is an openion in opposition to the thesis of Sauer (1950, 1956). Recent hydroclimatological research concluded that the Pampa should have a forest climate, i.e.mesophytic forest growth in the NE region, a transitional forest in the central region, and treeless steppe-like grassland in the W region, and extensive natural grassland which corresponds with an edaphic climax formation confined in the widespread azonal sites (Henning 1988). The concurrence between root systems of grasses and trees in the soil at given sites has also been intensively investigated, and as a result, it has become clear that the dominance in such a situation lies with the soil condition. In general, grasses dominate if soils are heavy, and trees dominate in light soils. In the Pampa, the boundary between grassland and woodland is approximately in accordance with that of heavy (in the east) and light (in the west) soils. Microscopic research on the soil, especially the humus, also gained remarkable results considering the former vegetation on the Pampa (Walter 1966, 1967; Wilhelmy and Rohmeder 1963; Troll 1968 etc.). Surrounding the Pampa are woodlands whose physiognomies are quite similar; however, their adaptabilities to climatic and hydroclimatic environments differ greatly, which complicated the Pampa problem (Walter 1967). It is certain that the results obtained by research on the Pampa problem contributed to the promotion of grassland studies elsewhere in the world and in turn on the Pampa. However, various problems regarding grassland have been raised with time. As is generally known, there are many research papers on the origin of savannas of the world, including Kadomura's (1984), Haruki's (1984) and Tamura's (1988) papers. The identification of climatic types on the basis of the effective method (for instance “savanna climate”) has been seriously criticized (Waibel 1948; Parsons 1955; Puson 1963; etc.). This and other methods must be re-examined.