522 IOWA ACADEMY OF SCIENCE 



LARIX AMERICANA Michx. Tamarack, Larch. 

 Leaves decidedly three-angled. 



Resin ducts obscure, but present at extreme edges of leaf. They 

 consist of an opening in a cluster of hypodermal cells. 



Vascular bundles surrounded by a definite sheath of round un- 

 lignified cells. Xylem bands small and divided. A very 

 few isolated lignified cells present in pith. 



Hypodermal cells present in small groups at lateral edges of leaf, 

 also one layer along dorsal and ventral midrib. Not lignified. 



Epidermal cells small, round and unlignified. 



Walls of parenchyma deeply infolded. 



Material from trees on Campus of Iowa State College. 



LARIX OCCIDENTALS Nutt. Tamarack. 

 Leaves more or less flat, keeled below. 

 Resin ducts none. 



Vascular bundle surrounded by a definite sheath of round, lig- 

 nified, loose joined cells. Xylem in excess of phloem with a 

 band of lignified cells extending from xylem through phloem 

 to a group of lignified strengthening cells below. Xylem bands 

 slightly separated. 



Hypodermal cells in a small group at lateral angles, also one 

 layer present along dorsal and ventral midrib. Lignified. 



Epidermal cells large, round and lignified. 



Parenchyma walls infolded. 



Material from University of Washington. 



Plate XXXIX. 



Figure 1'. — Section of leaf of Larix americana. 

 Figure 1". — Section of leaf of L. occidentalis. 

 Figure 2".— Section through stoma of L. occidentalis. 

 Figure 3'. — Section through resin duet of L. americana. 

 Figure 4'. — Section of vascular cylinder of L. americana. 

 Figure 4". — Section of vascular cylinder of L. occidentalis. 



