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over plants grown without competition (P < .05). Plants suffering from both root and shoot competition were not significantly smaller than those suffering from root competition only, but they showed the greatest size variability. In plants competing both above and below ground, root competition accounted for the reduction in mean plant size, but shoot competition accounted for the increase in size inequality. The results support the hypothesis that competition for light is "asymmetric" and that the observed increases in plant size variability with increasing density may have been primarily due to competition for light.There may be situations in which competition for nutrients is also asymmetric, i.e., situations in which nutrients can be preempted by individuals with larger roots. Because a leaf is shaded only by leaves above it, competition for light appears to be inherently asymmetric.Acknowledgments: