MORPHOLOGICAL STUDIES OF THE ROOT OF RED PINE, PINUS RESINOSA I. GROWTH CHARACTERISTICS AND PATTERNS OF BRANCHING

Abstract

Observations were made of the seasonal root growth behavior under natural conditions and under controlled conditions in plant observation boxes. Under natural conditions root growth conformed to the commonly reported pattern of a surge of growth in the spring, a mid‐summer low, and a renewed burst in the fall. Growth of individual roots was cyclic. Growth patterns ordinarily varied according to root diameter and branching and in the plantations were modified by soil moisture conditions. Observations of roots during periods of constant elongation showed that the distance from the root apex to the first lateral root primordium varied directly with growth rate. Laterals did not arise in strict acropetal succession, and lateral root abortion was common, particularly in large‐diameter, fast‐growing roots. Observations of root initiation in relation to seasonal growth increments and to dormancy structures showed an increase in numbers of laterals on both the proximal and distal portions of a seasonal increment.