550 IOWA ACADEMY OF SCIENCE 



PSEUDOTSUGA MACBOCARPA Mayr. Hemlock. 



Leaves flat, grooved above, keeled below, edges tending down- 

 ward. % inch to li/4 inches long. 



Resin ducts 2, lateral, lignified where touching ventral epidermis. 



Vascular bundle surrounded by a most pronounced bundle 

 sheath, cells of sheath lignified. Xylem appears as one bundle 

 with only a slight demarcation. Lignified strengthening cells 

 present below phloem and a wide band of lignified cells ex- 

 tend from xylem through center of phloem. 



Hypodernial cells present in one layer around entire peri- 

 phery. Walls lignified and very thick. 



Cells of epidermis mammillated. 



Stomata on ventral surface. 



Material from Herbarium of Iowa State College ; from San Ber- 

 nardino. California, and from State House grounds, 

 Sacramento, California. 



Plate LIII. 



Figure 1. — Section of leaf of Pseudotsuga macrocarpa. 



Figure 2. — Section through epidermis of leaf of P. macro- 

 car pa. 



Figure 3. — Section through resin duct of leaf of P. macro- 

 carpa. 



Figure 4. — Section through vascular cylinder of leaf of P. 

 macrocarpa. 



Note : The distinguishing feature between the leaves of the 

 two species of Pseudotsuga consists in the presence of a continu- 

 ous band of heavy walled, lignified, hypodermal cells in the leaf 

 of P. macrocarpa and the absence of the same, except along the 

 midrib, in P. mucronata. This fact tallies with the environ- 

 mental conditions under which the trees grow, as P. macrocarpa 

 lives under more xerophytic conditions than P. mucronata. 



