Behaviour of hard and permeable seeds of Abutilon theophrasti Medic. (velvetleaf)

Summary Experiments were carried out on seeds of Abutilon theophrasti (velvetleaf) to examine the germination behaviour of hard (impermeable) and soft (permeable) seeds and to test various physical and chemical treatments against hardseededness. There was no evidence, in fresh or in old seeds, of leachable germination inhibitors or of leachable compounds affecting hardseededness. Marked differences were found between hard and soft seeds in respiration and leakage. Oxygen uptake was negligible in hard seeds. A rapid efflux of K + ions from hard and soft seeds was detected during the first minutes of immersion. Subsequently, the rate of leakage of hard seeds decreased markedly. After 4 h of imbibition, conductivity measurements differentiated individual hard and soft seeds. Abrasion, percussion and immersion in sodium hypochlorite had no effect on hard seeds, but mechanical scarification and immersion in sulphuric acid reduced hardseededness. Gamma radiation did not affect the hard coat but damaged the embryo. A. theophrasti seeds were exposed to organic solvents such as acetone. ethanol and methanol, and to pesticides such as butylate, EPTC, metham‐sodium, vernolate and methyl bromide, in liquid or gaseous phase. Some of the treatments reduced germination of soft seeds, but none, even methyl bromide, had any significant effect on the number or viability of hard seeds, proving their complete impermeability.