Abstract
Sap sugar levels were determined for 300 sugar maple, Acersaccharum Marsh, trees. The 10 trees highest and lowest in sap sugar were sacrificed and attempts were made to calculate abundance and size of parenchyma flecks caused by Phytobiasetosa (Loew) and ray tissue per unit of xylem. Flecks occurred in up to 0.2% of the xylem, but there was no significant difference between fleck number or xylem-fleck ratio and sap sugar levels. Fleck numbers decreased with tree height; largest flecks were observed at the root collar and 8–12 m from the ground. This suggests that all P. setosa larvae do not mine from twigs in the crown to the roots, but that some mature and exit at the base of the tree crown. Trees high in sap sugar had significantly more ray tissue per unit of xylem than those low in sap sugar, a major factor in determining sap sugar concentrations.
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