GROWTH STUDIES OF THE ROOT OF INCENSE CEDAR, LIBOCEDRUS DECURRENS. II. MORPHOLOGICAL FEATURES OF THE ROOT SYSTEM AND GROWTH BEHAVIOR

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Abstract
Wilcox, Hugh. (State U. Coll. of Forestry, Syracuse, New York.) Growth studies of the root of incense cedar, Libocedrus decurrens. II. Morphological features of the root system and growth behavior. Amer. Jour. Bot. 49(3): 237–245. Illus. 1962.—The common pattern of root growth in incense cedar involves a rush of growth in the spring, a midsummer low, and a renewed surge in the fall. Not all of the roots of a seedling grow at any one time, but some roots are growing while others are dormant. The cycle of growth of an individual root varies from 3 to 9 weeks or more; the large‐diameter roots and the principal laterals grow more rapidly and for longer periods than the smaller‐diameter roots or those of higher order. Roots of various growth rates were treated with different concentrations of indoleacetic acid and with extracts from growing and dormant roots. Roots show adaptation to the lower concentrations of IAA, with subsequent stimulation of elongation occurring in solutions of concentrations 10‐6 through 10‐9 moles/liter of IAA. Roots which have been growing slowly at the time of treatment are more strongly stimulated than those which have been growing rapidly. Roots do not become adapted to root extracts but remain inhibited by all such treatments. A study of the anatomical features of dormant and actively growing roots provides indirect evidence that a number of hormonal factors are operating to control the various physiological activities associated with the growth of the root.