526 IOWA ACADEMY OF SCIENCE 



KEY TO PICEA. 

 1. Without resin ducts. 



2. Leaves 4-angled. Three to four rows of stomata on 

 each side of leaf. Parenchyma walls smooth 



P. canadensis 



2. Leaves flattened. Two to three rows of stomata on 

 each side of mid-rib on lower surface. Numerous 



stomata on upper surface P. sitchensis 



1. With resin ducts. 



2. Resin ducts more or less touching lateral angles 

 Leaves 4-angled. Four to seven rows of stomata 



on each surface P. parryana 



2. Resin ducts touching ventral sides. 



3. Leaves more or less 3-angled. Four to five 

 rows of stomata on each upper surface, no 



stomata on lower surface P. Breweriana 



o. Leaves 4-angled. 



4. Resin ducts very large, as large as vascu- 

 lar cylinder (in some leaves one or 

 both wanting). Three to five rows of 

 stomata on each surf ace... P. Englemanni 

 4. Resin ducts small. 



5. Two layers of cells lining resin 

 ducts. Four rows of stomata on 

 each upper surface. Two rows 



on each lower surface P. ruhens 



5. One layer of cells lining resin ducts. 

 Four to five rows of stomata on 

 each upper surface. Two to 

 three rows on each lower sur- 

 face P. mariano 



PICEA MARIANA B. S. & P. Black Spruce 



Leaves 4-angled, 14 to 3 /4 inch long. 



Resin ducts 2, small, lateral, touching ventral epidermis, one 

 layer of lignified cells lining the duct. 



Vascular bundles — Xylem obscurely separated, cells of pith 

 largely lignified, several large lignified strengthening cells be- 

 low phloem. Cells of bundle sheath lignified at their junc- 

 ture. 



Hvpodermal cells in one layer around entire periphery, ligni- 

 fied. 



Epidermis lignified on inner wall. 



Parenchyma walls corrugated. 



Stomata 2 to 3 rows on lower side 

 4 to 5 rows on upper side. 



Material from Campus of Iowa State College. 



Plate XLT. 



Figure 1. — Section of leaf of Picea mariana. 



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

 P. mariana.. 



Figure 3. — Section through resin duct of leaf of P. mariana. 



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

 mariana. 



