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 (VRC) in same condition on right; this is 

 longitudinal view of same canal as is shown in cross section, Plate LVI, figure i. 



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. 



