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Summary

Experimental evidence is given for poplar cuttings (Populus x robusta Schneid.) of the role of dormant and nondormant buds to root initiation. Chilling treatments shortened bud dormancy and greatly increased the emergence of pre-formed roots from stem cuttings, but caused a smaller increase in numbers of wound-roots. With terminal popular cuttings greater root numbers were obtained when, after excision, a warm treatment preceded chilling. Chilling only induced a large increase in the number of wound-roots on terminal apple cuttings (Malus cv. Mailing II), if steeped in indolyl butyric acid immediately after the chilling treatment.

A greater amount of auxin was found in chilled than in unchilled poplar cuttings five weeks after the end of chilling.

Endogenous auxin levels at the base of both intact and disbudded, chilled cuttings of poplar were high at the time when roots were about to emerge from the cortex, but were low 15 days later when the roots were several centimetres in length.