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It has been shown that dense monospecific, even-aged stands of plants become progressively thinned as the survivors increase in size. The relationship between mean weight per plant (w) and the density of survivors (p) can be written as w= Cp-32 (Yoda et al. 1963) where C is a constant. This relationship has been shown to hold for a wide range of species including mosses, herbs and trees (Gorham 1979, White 1980). When log w is plotted against log p, the values are found to lie around a line of slope of ca.-1.5. The-3/2 power law of Yoda et al. has been used to describe the relationships during thinning between two plant species in mixtures (White and Harper 1970, Bazzaz and Harper 1976). White and Harper (1970) found that crowded mixed populations of Brassica napus L. and Raphanus sativus L. closely followed the-3/2 power law when both of these species were considered together. The exponent of p …