KEY TO GENERA AND SPECIES 31 



(Fig. 53.) Sourwood, Sorrel-tree, Oxyden- 

 drum arboreum (L.) DC. 



NOTE. The Hop Hornbeam may be sought here 

 if the side veins of the blade are more curved 

 than usual. 



56. Fruit with a single central stone 

 which encloses a single seed 

 Cherry, Plum, Peach, 175. 



56. Fruit with the seeds in thin-walled 



compartments 57. 



57. Fruit less than \ inch thick June- 



berry, 158. 



57. Fruit f to 2 inches or more thick 

 Apple, Pear, 152. 



58. Leaf-stalk less than \ the length of Fig- S3- 

 the blade, or else the width of the 

 blade less than \ the length of the blade* 

 Willow, 91. 



58. Leaf-stalk more than \ the length of the blade, 

 or else the blade nearly as wide as long *- 

 Poplar, 98. 



* Exceptionally narrow-leaved forms of the Balsam Poplar 

 may be distinguished, from Willows, by the strong balsamic 

 odor of leaves and buds, and by the metallic-looking sticky lower 

 surface of their leaves. 



