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The mesophyll region is composed of chlorophyll-bearing, parenchyma 
cells. These cells differ from the corresponding ones of the pine, in that 
they do not show that characteristic infolding of the cell wall. The eell 
walls are smooth, more like the parenchyma of an ordinary leaf. It is 
within this region that the resin ducts occur. These ducts may be either 
peripheral when they lie directly under the epidermis, or medial when 
they lie entirely surrounded by the parenchyma. These lie parallel to the 
longer axis of the leaf and are surrounded by a series of strengthening 
cells. Lining the inside of the duct is a single layer of secretory cells. 
PICEA MARIANA. 
D Ducts. M Mesophyll. 
B Bundle sheath. S Strength. cells. 
F Fibro-vas. bundles. E Epidermis. 
A Strength. cells within sheath. 
