544 IOWA ACADEMY OF SCIENCE 



TSUGA HETEROPHYLLA Sarg. Hemlock. 



Leaves flat, edges tending downward, 14 to % inch long, grooved 

 top. 



Resin duct 1, large, lined with. 2 layers of cells, inner layer con- 

 sisting of large, round, unlignified cells. 



Vascular bundles enclosed in a sheath of large loose cells ; within 

 the sheath, in addition to vascular bundle, lie a few lignified 

 cells below and at each side of phloem. 



Hypodermal, lignified cells present along lateral edges of leaf 

 and along dorsal groove. Walls of guard cells lignified. 



Stomata in bands of 7 to 9 rows along each side of midrib. 

 Parenchyma along ventral surface of leaf, having cells arranged 

 with greatest length laterally. 



Material from University of Washington, Seattle. 



Plate L. 

 Figure 1. — Section of leaf of Tsuga lieterophylla. 



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

 T. heterophylla. 



Figure 4. — Section through vascular cylinder and resin duct 

 of leaf of T. keterophyUa. 



