Proceedings of the Ohio State Academy of Science 91 



KEY TO THE GENERA OF TREES IN THE WINTER 



CONDITION. 



Based mainly on twig and stem characters. The num- 

 ber following the genric name refers to the list number. 

 I. Foliage leaves persistent and usually evergreen. 2. 



1. Foliage leaves deciduous each year. 11. 



2. Foliage leaves needle-shaped, subulate, narrowly linear, 



or scale-like; conifers. 3. 



2. Foliage leaves with expanded blades, netted veined. 8. 



3. With dwarf branches, each bearing 2-5 foliage leaves. 



Pinus. (2). 



3. Without true dwarf branches. 4. 



4. Leaf buds scaly. 5. 



4. Leaf buds not scaly, naked. 7. 



5. Leaf scar not on a sterigma, prominent, circular; leaves 



flat. Abies. (6). 



5. Leaf scar on a sterigma, the base of the leaf remaining 



as a scale on the twig. 6. 



6. Leaves flat, those on the upper side of the twig much 



shorter than the lateral ones. Tsuga, (5). 



6. Leaves more or less 4-sided, spreading in all directions. 



Picea. (4). 



7. Foliage leaves small, scale-like, appressed, opposite, 4- 



ranked, closely covering the twigs which are decidedly 

 flattened and fan-like ; leaves of two shapes, the dorsal 

 and ventral broader and less acute than the lateral 

 ones ; scales of the carpellate cone not peltate. 



Thuja. (8j. 



7. Foliage leaves small, scale-like, appressed, opposite, 4- 

 ranked, closely covering the slightly flattened twigs 

 which are not very fan-like ; leaves nearly or quite 

 similar ; scales of the carpellate cone peltate. 



Chamaecyparis. (9) . 



7. Foliage leaves of two types, scale-like and subulate, op- 

 posite or in threes ; the scale-like leaves 4-ranked, ap- 

 pressed, causing the twigs to appear quadrangular, the 



