Leader, Needle, Cambial, and Root Growth of Certain Conifers and Their Interrelations

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Abstract
In southern New Hampshire, leader elongation of pl.nus resinosa began in late April, reached a max. June 10, and ceased in mid-Aug. Of this growth, 96% occurred during the 60-day period, May 15-July 15. P. strobus and P. rigida follow a similar seasonal course of leader elongation. pl.cea glauca and Abies balsamea began and ceased growth about 2 weeks later than the pl.ne spp. Leader elongation of P. resinosa during the night showed a positive correlation with min. temp. Needles located at the base of the leader pasa through their grand period of growth earlier than those near the tip of the leader. Needle elongation in P. resinosa began May 15, reached a maximum late in June, and ceased in early Sept.; 94% of the growth occurred in the 60-day period June 10-Aug. 10. P. strobus and P. rigida had a sjmilar needle development. Needles developed from a meristematic region at their base. No elongation occurs after the 1st growing season. Cambial growth in P. resinosa started early in May, reached double maxima on June 2 and July 9, and ceased early in Oct. There is an interrelation between the different growing activities of the tree. The first surge of growth in the spring of the roots, leader, and cambium occurred at the same time, followed by max. needle growth and a 2nd max. cambial growth and a 2d max. root growth. There is probably an internal balance between the metabolic activities of the different growing regions of the tree which determines the time of their max. development. An abundance of stored food is probably responsible for the 1st surge of growth. As these reserves become depleted the limited supply of currently elaborated food is inadequate to maintain this rapl.d growth rate in all the meristematic regions at the same time.

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