96 Proceedings of the Ohio State Academy of Science 



most cases pubescent ; some species with characteristic 

 transverse self-pruning scars on the twigs, others with 

 corky ridges. Ulmus. (23). 

 37. Bark scaly, fine-furrowed, the furrows usually somewhat 

 spiral ; bud scales green with brown tips, nearly 

 glabrous ; staminate catkins exposed in winter. 



Ostrya. (17). 



37. Bark of trunk and larger branches separating into papery 



or leathery sheets; catkins in winter. Betula. (18). 



-38- 



38. With 2 or more superposed axillary buds; all except 



I may be very small. 39. 



38. Axillar}^ buds single or 2 or more side bv sMe ; not 



superposed. 46. 



39. Pith diaphr.agmed, with air cavities. 40. 



39. Pith diaphragmed but solid ; bundle scars 3 ; stipular 

 scars none. Nyssa. (76). 



39. Pith not diaphragmed, solid. 41. 



40. Pith large, brown; twigs thick, with large leaf scars 



and 3 prominent bundle scars. Juglans. (14). 



40. Pith rather small, white or greenish ; leaf scars semi- 



circular ; outer bud scales about 2. 



Mohrodendron. (68). 



41. Buds partly sunken, hardly projecting beyond the sur- 



face ; terminal bud self-pruned or tips of branches 

 withering. 4.2. 



41. Buds not sunken in the epidermis. 43. 



42. Leaf scar not surrounding the axillary buds ; pith large, 



chocolate-colored ; twigs robust, polished, mottled 

 white and purplish-brown. Gymnocladus. (46). 

 42. Leaf scar surrounding the Axillary buds, quadrangular 

 U-shaped ; bark with pungent odor ; pith white. 



Ptelea. (50). 



42. Leaf scar covering the axillary buds ; pith small ; twigs 



brown, polished, often zigzag. Gleditsia. (45). 



43. Pith cylindrical or nearly so. 44. 



