54 TREES OF THE NORTHERN UNITED STATES 



N. Leaves broad for the length, generally doubly serrate or 

 wavy and serrate ; shrubs, rarely tall enough for trees. (P. ) 

 N. Not included in the above. (O.) 



O. Leaves 3 or more times as long as wide, widest near the 

 center; fruit a round, prickly bur with 1-3 horny-coated 



nuts 89. Castanea. 



O. Leaves widest near the sharply serrate tip, narrow and en- 

 tire near the base ; fruit small pods in terminal racemes ; 



small tree or shrub 53. Cleihra. 



O. Leaves widest near the base, usually small ; bark scaling off 

 like the Buttonwood; fruit axillary, solitary, small (i in.) 

 roundish, dry drupes. A cultivated species, has rather large 



leaves, widest near the center 75. Planera. 



P. Fruit an open oval woody catkin or cone, remaining on the 



plant through the winter 84. Alnus. 



P. Fruit a rounded stony nut, in green leafy edged bracts ; shrubs 



or small trees 85. Corylus. 



Q,. Usually aromatic ; bark dotted on the spray and with hori- 

 zontal marks on the trunk, peeling off in thin, often papery 



layers 83. Betula. 



Q,. Bark not peeling off in thin layers. (R. ) 

 R. Leaf -buds long and slender ; fruit a small prickly bur with two 



triangular, horny-coated nuts ; large trees 90. Fagus. 



R. Fruit an elongated catkin with large leaf -like bracts; bark 



close, gray, on a grooved trunk 87. Carpinus. 



R. Fruit a hop-like catkin ; bark brownish, finely furrowed 



86. Ostrya. 



S. Plant more or less thorny ; shrub or small tree ; fruit rounded 



berries ending in persistent calyx-lobes 38. Cratsegus. 



S. Plant not thorny. (T.) 

 T. Leaf deeply pinnatifid, usually with the basal lobes completely 



separated ; cultivated 37. Pyrus. 



T. End of leaf as though cut off; sides with one large lobe ; mar- 

 gin entire ; large tree 2. Liriodendron. 



T. Lower leaves three-lobed, heart-shaped at base, upper merely 



ovate, margin entire ; small tree or shrub 66. Clerodendron. 



T. Not as above ; leaves usually many-lobed. (U. ) 

 TT. Leaves thin; bark of trunk peeling off in thin horizontal 



strips 83. Betula. 



U. Leaves thin ; leaf -buds long, slender, sharp-pointed ; bark 



smooth, not peeling ; cultivated 90. Fagus. 



U. Leaves thickish ; bark roughish ; fruit an oval woody cone, 



remaining on through the year 84. Alnus. 



TJ. Leaves thick ; fruit an acorn 88. Quercus. 



