Germination Preventing Mechanisms in Iris Seeds

The different germination behaviour of the seeds of two irises, Iris lorteli and I. atropurpurea was found to be due to the different mechanical resistance of the integument, at the micropylar end, to radicle protrusion. A pressure of 135 atm was necessary in l. lorteli seeds for radicle protrusion, while in I. atropurpurea 77 atm was sufficient. In contrast Pancratium maritimum required a pressure of only 10 atm. The outer integument of seeds of l. lorteti was found to contain a compound which was toxic to the germinated embryo but did not act as a germination inhibitor. Extracts of the endosperm also had a slight germination inhibiting effect. An interaction between this weak inhibitor and the effect of the testa could not be ruled out completely. A test assay for germination using excised embryos was developed. A method for germination of Iris seeds, by cutting off the outer integument at the micropylar end, was developed and is being exploited commercially.