Some Observations on the Effect of Drought on the Growth of Pinus Radiata D. Don

SUMMARY Detailed observations have been made of the developing growth rings in a 30 year old plantation of Pinus radiata during 1961–62. The occurrence of a sharp drought period followed by heavy rain and favourable growing conditions resulted in the formation of a “false ring”. Weekly samples of the cambial region showed that cell division ceased and the cambium appeared inactive at the height of the drought. Rapid cell division occurred after the rain, followed by an interval of several weeks before appreciable additions were made to the wood. The observations are discussed in relation to current theories on auxin regulation of physiological processes involved in wood formation.