Strach storage and radial growth in woody roots of sugar maple

The timing and pattern of starch storage and the timing of radial root growth in sugar maple, Acersaccharum, were observed with micro- and histo-chemical techniques from May to December. Results of initial monthly observations showed that starch deposits were very low or depleted in May shortly after budbreak but were fairly heavy by mid-July. A starchless ring of xylem was evident on some roots in mid-July and all roots in mid-August but was not visible in early November. Data from weekly observations indicated that the starchless xylem resulted from new tissue development that began in early July after substantial starch storage. The major portion of growth occurred by early September. The new xylem had no visible starch until mid-August. Initially, starch deposits developed in new xylem cells nearest to the previous annual ring. Starch appeared first in the ray parenchyma, next in the xylem fibers adjacent to vessels, and then in xylem fibers more distant from the vessels. By late September, the outer ring of xylem was no longer distinctly different from the older tissue. In contrast with the stem, where radial growth precedes or coincides with carbohydrate storage, substantial storage of carbohydrates preceded radial growth in the roots.