Induction of resin pockets in seedlings of Pinus sylvestris L. by mechanical bending stress during growth

Mechanical bending stress due to wind exposure has been suggested to be of major importance for induction of resin pockets in gymnosperm trees. In thi s study, this idea was tested experimentally by applying bending stress to 1-year-old internodes of five-year-old Pinus sylvestris L. seedlings during dormancy and/or growth. The stems were bent manually to 30 degrees from th eir original upright position at regular intervals. About 30 % of the stems that were bent during growth were wounded in the xylem, whereas no woundin g was observed in control stems or stems bent during dormancy. Similarity o f these wounds to naturally-occurring resin pockets leads us to conclude th at exposure of seedlings to mechanical bending stress due to wind during gr owth can be a source of formation of resin pockets.