80 Proceedings of the Ohio State Academy of Science 



KEY TO THE GENERA OF TREES IN THE SUMMER 



CONDITION. 



Based mainly on leaf and twig characters. The number 

 following the generic name refers to the list number. 



1. Foliage leaves with expanded blades, netted-veined. 8. 

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

 or scale-like ; conifers. 2. 



1. Foliage leaves fan-shaped with dichotomous venation, a 



number on thick, wart-like, persistent dwarf branches. 

 Ginkgo. ( I ) . 



2. With typical dwarf branches, persistent for more than 



I year. 3. 

 2. With feather-like dw.arf branches, deciduous each year, 

 the linear leaves spreading into 2 ranks. Taxodium. (7). 



2. Without dwarf branches. 4. 



3. Dwarf branches small, self-pruned, with 2-5 foliage 



leaves. Pinus. (2). 



3. Dwarf branches thick, wart-like, persistent, with nu- 



merous deciduous leaves. Larix. (3). 



4. Leaf buds scaly ; leaves scattered. 5. 



4. Leaf buds not scaly, naked ; leaves opposite or whorled. 7. 



5. Leaf scar on a sterigma, the twigs covered with scales 



representing the leaf bases. 6. 



5. Leaf scar on the bark ; twigs without scales ; leaves 



flat. Abies. (6). 



6. Leaves f^iat, those on the upper side of the twig much 



shorter than the lateral ones; trees. 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. (8). 



