PLATE LVIII 
Open and closed horizontal canals in sap wood. 
Fig. i.—Open canal in tamarack ( TE ) thick-walled epithelium. 
Fig. 2.—Partly closed canal with distended epithelial cells ( DE ) in Douglas fir. 
Fig. 3.—Young canal which has never opened in western white pine. Cells with 
protoplasm and nuclei. Vertical canal ( VivC) in same condition on right; this is 
longitudinal view of same canal as is shown in cross section, Plate LVI, figure 1. 
Fig. 4.—Open canal in red spruce surrounded by thick-walled epithelium (TE). 
Fig. 5.—Partly closed canal in red spruce. TE, thick-walled, and DE, thin- 
walled distended epithelial cells. 
Fig. 6.—Closed canal in Engelmann spruce. From old sapwood. The epithelial 
cell has completely closed the canal and its wall has become thickened. 
