SOME NORTH AMERICAN CONIFERS 521 



ARTIFICIAL KEY TO CONIFERS BASED ON LEAF SECTIONS. 



I. Leaves 3 to 4-angled, or if compressed without a dorsal groove. 

 Vascular cylinder surrounded by a conspicuous 

 bundle sheath. Vascular bundle obscurely divided. 

 Resin ducts present or absent. 



2. Walls of parenchyma deeply infolded / 



2. Walls of parenchyma not infolded, smooth or only 



slightly corrugated Picea 



I. Leaves more or less flattened, usually grooved above. 

 2. One central resin duct. 



3. Two vascular bundles Tsuga 



3. One vascular bundle, leaves very small, resin duct 



inconspicuous Taxodium 



3. One vascular bundb . haves very large, resin duct 



large Tu m ion 



2. Two lateral resin duets. 



3. Vascular cylinder surrounded by a conspicuous 



bundle sheath. One vascular bundle. . . Pseudotsuga 

 3. Vascular cylinder .surrounded by a group of pith- 

 like cells or an inconspicuous bundle sheath. 



Two distinct bundles ibies 



2. Three resin ducts Sequoia sempervirens 



2. No resin ducts. One vascular bundle. Walls of epi- 

 dermal cells and cutin deeply mammillated Taxus 



KEY TO LARIX. 



Leaves 3-angled or keeled. 



2. Leaves distinctly 3-angled. Obscure resin ducts in 



lateral edges of leaf L. arm i'v ana 



2. Leaves slightly 3-angled or flat with keel on ventral side. 



No resin ducts L. occidentalis 



Leaves 4-angled L. Lyallii 



