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The diallel cross analysis first proposed by Jinks in 1954 iS now generally accepted as a useful and powerful device for investigating the nature of genetic differences controlling quantitative characters. It has been widely used to investigate differences between inbred lines and between varieties within numerous species. It is clear that the analysis could also be useful in the investigation of variation between more distantly related parents or populations, in particular between species, when it could be expected to throw some light on the nature of the genetic differences by which separate species have diverged during the course of their evolution. The results should enable us then to describe, with respect to particular characters, the divergence of specific genotypes in strictly genetic terms, that is with respect to the dominance, interaction and other properties of genes or gene systems which distinguish them. The present brief report demonstrates the use of such a diallel analysis applied to one of many characters being investigated in species within the genus Secale. The character in question is the average length of time between germination and the development of the second leaf in genotypes produced from crosses within and between the species. The seeds were obtained from crosses between at least three pairs of plants within and between each species. Because of the shortage of seeds, particularly in some interspecific crosses, the seeds were mixed. Seeds were then sown in two replicates with io seeds each. 202 577 NOTES AND COMMENTSThere was excellent correspondence between replicates and an analysis of variance showed highly significant differences between genotypes (P=