Crosses were made, in all combinations, between 2 parental genotypes of Linum and their reciprocal F 1 hybrids. The parents and progeny obtained were grown in controlled environmental conditions and sampled at 35 and 70 days after germination to determine, on an individual plant basis, total plant fresh weight and peroxidase activity of main stem tissue. Peroxidase activity required transformation to a log10 scale, whereas the original linear scale was satisfactory for plant weight. There was no correlation between plant weight and corresponding peroxidase activity. Pronounced heterosis appeared in the F 1's for both characters at sample 1, but this heterosis had declined at sample 2 and in the F 2's. Heterosis operated in a positive direction for plant weight and in a negative direction for peroxidase activity. No consistent differences were found amongst the variances of segregating or non-segregating generations for either character.