Plant population structure and aphid parasitism: changes in barley monocultures and mixtures.
Two cultivars of barley, one resistant and one susceptible to aphids, were grown in pots in mono- or mixed culture in the laboratory, and either infested with aphids (Schizaphis graminum (Rond.)) or kept free of them. The frequency distributions of seed weight, dry weight and plant height were then analysed for three harvests. Seed weight and shoot weight were normally distributed at all harvests, though non-significant departures from normality in shoot weight occurred in those infested with aphids and these departures were hastened by genetic heterogeneity within the populations; the absence of significant skewness and bimodality was explained on the basis of little variability in relative growth rates among the plants. Plant height was not normally distributed at any period but was significantly skewed and leptokurtic whether or not aphids were present.