The Effects of Shaking on Extension Growth of Pinus contorta Douglas

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Abstract
Subjecting young plants of P. contorta to continuous shaking outdoors caused a 20 per cent reduction in the extension of leading and lateral shoots, and a 10 per cent reduction in the extension of needles. The ratio of the final length of the laterals to that of the leaders (‘apical control’) was unaffected by shaking as was the radial growth of the stems. Shaking for only 24 minutes per day had almost the same effect as shaking continuously. Shaking in 1978 had no effect on fascicles produced in 1979 or on the response to shaking in 1979. The effect of shaking could not be attributed to an induced water stress. To see whether the shaking treatment affected cell division or cell expansion an examination was made of the pith parenchyma. The shorter stems from the shaken treatment contained fewer cells than the controls, though cell size was not much affected. The results of the shaking experiment were very similar to the results of the wind tunnel experiment described in the previous paper.