Proceedings of the Ohio State Acadeniy of Science 87 



—53— 

 53. Base of petiole covering the axillary bud ; twigs with 

 stipular rings. Platanus. (31). 



53. Axillary buds usually evident ; twigs without stipular 



rings. 54. 



54. Leaves 2-ranked. 55. 



54. Leaves not 2-ranked. 60. 



55. Leaves entire, round-heart-shaped. Cercis. (44). 



55. Leaves serrate, dentate, or lobed. 56. 



56. Pith usually in transverse plates ; leaves ovate-lanceolate, 



inequilateral, taper-pointed. Celtis. (25). 



56. Pith solid, not diaphragmed. 57. 



57. With milky s,ap. 58. 



57. AA/'ithout milky sap. 59. 



58. Twigs gray or brown, glabrous or nearly so;, leaves 



pubescent or glabrous beneath. Morus. (26). 



58. Twigs grayish-green, downy ; leaves tomentose be- 



neath. Broussonetia. (28). 



59. Leaves not inequilateral ; vascular bundles in base of 



petiole 3. Betula. (18). 



59. Leaves inequilateral at the base; vascular bundles in 



base of petiole several, scattered. Tilia. (61). 



60. Leaves more or less star-shaped, with 3-7 long pointed 



serrate lobes, strongly aromatic when crushed ; pith 

 5-angled. Liquidambar. (30). 

 60. Leaves entire or three-lobed, bark spicy-aromatic ; in- 

 ternodes very unequal. Sassafras, (35). 



60. Leaves crenate, serrate, dentate, or lobed, not star- 



shaped and not spicy-aromatic. 61. 



61. Pith 5-angled; trees usually with resinous buds; leaves 



usually broad biased. Populus. (11). 



61. Pith cylindrical or nearly so; usually with prominent 



typical thorns. Crataegus. (41). 

 —62— 



62. Pith diaphragmed, with cavities; large trees with pin- 



nate leaves. Juglans. (14). 



