Nutation in Pinus Sylvestris

Abstract

1. A long series of observations on the elongating shoots of Pinus sylvestris showed that during the elongating period the new shoots are subject to nutations, which are caused by differentiation of the water pressure on the different sides, resulting in growth curves in the direction where the turgidity was least. The two agents that thus operated locally to decrease turgidity were direct sun and wind. In the absence of either, the shoots were erect. 2. The same effects take place regularly upon the slender-shooted Pinus banksiana and P. strobus, but were not present on the stout-shooted P. laricio and P. ponderosa. In general the wind seemed to have a greater effect than the sun, as long as it was strong enough to rustle leaves of ordinary trees. The effects were greatest when wind and sun operated together, but changes from one position to another following changes of the factors could be quite rapid.