Alginate lyase-lysate (A.L.L., Algin-Oligo(R)), which had been prepared by degrading sodium alginate by alginate lyase, was found to have a growth-promoting effect on the elongation of barley roots, and especially that of the radicle, the effective concentration of A.L.L. for elongation of the roots being 100-3000μg/ml, with no inhibition at the highest concentration. When a radicle was brought into contact with A.L.L., it responded by initiating elongation within 2 to 4h. The elongation rate increased from 2.9mm/h to 5.3mm/h. Treatment with A.L.L. resulted in about a 2-fold increase in the alcohol dehydrogenase activity of the control under hypoxic conditions.