About one-fifth of the national fruit and vegetable production is sold in the biggest city in Mexico through the most important terminal market: the produce wholesale center in Mexico City (CEDA-CM). This huge market, opened at the end of 1982, is not only the crucial urban supply point where the retailers get the produce that is offered directly to the consumers, but is also an important redistribution center for other enterprises or regions in the country. Because of its size and the number of merchants operating there, it is considered the biggest wholesale market of its kind in Latin America.
While the size and types of traders vary, there is, nevertheless, a high degree of commercial concentration within the market. This is exemplified by the fact that ninety wholesalers (or 4%) control 80% of the marketed volume of fruits and vegetables (Echánove 1998:7). They hold the strategic position of supplying food to the most important urban concentrations not only in Mexico, but the whole world, and consequently wielding enormous power in the market.
A purchasing network formed by these large wholesalers in the rural areas is one of the factors that explain this situation. Unlike the case in similar markets in other countries, such as the United States, a great number of the merchants in the CEDA-CM are at the same time large agricultural producers. In addition, others have integrated themselves backwards to a lesser degree, in that they become packers or owners of agro- industrial production units.
The purpose of this article is to analyze the characteristics of the group of wholesalers at the CEDA-CM that concentrate on one of the important products of this market, namely, avocado. In this case study, we describe the supply mechanisms used by those agents. In order to do so, we follow the route of that product from the orchards to the traders' warehouses. The methods used here are participatory observation and direct interviews carried out during the last seven years among producers and their organizations, packers, middlemen, public and private officials of the state of Michoacan, the main avocado producing enterprise in Mexico, and the most important supplier of CEDA-CM. In addition, the largest suppliers in this market were also interviewed.
II. RESEARCH APPROACH
Although in the field of anthropology there are a large number of studies on producer and farmer markets articulated through trade to capitalist societies (Oswald 1979; Cook and Diskin 1976; Paré 1975), little has been written on urban markets and, still less, on the large wholesale markets. Several authors have analyzed the rural distribution systems focusing on the spatial aspect of the markets; mainly on trading between towns and rural communities to their food supply zone or 'hinterland'. Their methodological and theoretical bases are found on the geographic models, especially in the central place theory proposed in the 1930's by German geographers, Walter Christaller and August Losch.
Among the most important representatives of such a perspective are William Skinner (1964), who described the traditional rural marketing system in Szechwan, China, and Carol Smith (1974; 1977), who studied a market system surrounding the regional center of western Guatemala: Quetzaltenango. Other rural schemes of product distribution different from the central place model were developed by Johnson (1970), supported by Mintz' studies (1960) on the Haitian case, and by Appleby (1976) on the Puno community in Peru.
However, the purpose of our study is not about the spatial aspect of the supply system. In addition, the distribution schemes between the rural communities and the local and regional markets are very different from those present in the case of supply to big cities like Mexico City. On the one hand, we must point out that the assumptions of the above mentioned models cannot be generalized. Some of them (even distribution of the population and income, perfect competence, free product circulation, and regions without social or political barriers to trade) are unrelated to the real world. …