546 IOWA ACADEMY OF SCIENCE 



TSUGA MERTENSIANA Sarg. Mountain Hemlock. 



Leaves flat, grooved on top, edges tending down, 1-12 to 1 inch 



long. 

 Resin duct 1, small, central, on ventral side touching epidermis ; 



cells lining duct not in a definite layer. 



Vascular bundle enclosed in an obscure sheath of large, round, 

 loosely joined cells, xylem bundles small, separated by 1 or 2 

 rows of unlignified cells, groups of cells in pith on each side 

 of phloem lignified. 



Hypodermal cells present only at edges of leaf, cells lignified 

 also at point where duct and epidermis touch; guards cells 

 lignified. 



Stomata on both surfaces, 8 rows on each side of midrib on 

 ventral surface. 



Material from Jamaica Plains, Massachusetts. 



Plate LI. 



Figure 1. — Section of leaf of Tsuga mertensiana. 



Figure 2. — Section through epidermis and stomata of leaf of 

 T. mertensiana. 



Figure 4. — Section through vascular cylinder and resin duct 

 of leaf of T. mertensiana. 



