m. Trunk fluted ; fruit inclosed within 



a halberd-shaped involucre 



CARPINUS, p. 83. 



mm. Trunk not fluted; fruit not in- 

 closed within a halberd-shaped 

 involucre. 



n. Bark of trunk gray-brown, brok- 

 en into narrow, flattish pieces 

 loose at the ends; fruit in hop- 

 like strobiles... OSTRY A, p. 81. 

 nn. Bark of trunk white, yellow or 

 dark brown, platy or cleaving off 

 in papery layers; fruit not in 



hop-like strobiles 



BETULA, p. 84. 



kk. Leaf-blades almost as broad as they 

 are long. 



I. Lower side of leaves more or less 

 downy; sap milky; leaves not crowded 

 on short, spur-like brancblets ; fruit 

 berry-like, black. .. .MORUS, p. 135. 



II. Lower side of leaves glabrous; sap 

 not milky; leaves crowded on short, 

 spur-like branchlets; fruit a large, 

 green pome PYRUS, p. 142. 



ee. Margin of leaves distinctly lobed. 



f. Fruit an acorn QUERCUS, p. 96. 



ff. Fruit not an acorn. 



g. Leaves fan-shaped, with many fine veins radiat- 

 ing from the base of the blade. .GINKGO, p. 3. 

 gg. Leaves not fan-shaped, without many fine veins 



radiating from the base of the blade, 

 h. Leaf-lobes entire. 



i. Leaf-petioles 5-6 inches long; leaves lustrous 



above ; twigs not aromatic when bruised 



LIRIODENDROiN, p. 137. 



ii. Leaf-petioles about I inch long; leaves dull 

 above ; twigs spicy-aromatic when bruised 



SASSAFRAS, p. 139. 



hh. Leaf-lobes sinuate-toothed to serrate. 

 xxiv 



