KEY TO GENERA 25 



146. Twigs rather thick; leaf-scars large. . . Juglans, p. 61 



146. Twigs slender ;leaf-scars small. . . Celtis, p. 85 



147. Pith with firmer diaphragms at intervals. 148 



147. Pith without firmer diaphragms. 149 



148. Buds densely covered with reddish-brown hairs. . . Asimina, p. 97 



148. Not as above. . . Nyssa , p. 157 



149. Buds densely covered with reddish-brown hairs. . . Asimina , p. 97 



149. Not as above. 150 



150. Buds in hairy pits, . . Gymnocladus, p. 127 



150. Buds not in hairy pits. 151 



151. Pith angled; twigs corky-ridged. . . Liquidambar , p. 103 



151. Not as above. 152 



152. Sap milky. 153 



152. Sap not milky. 154 



153. Bud-scales 2 or 3. . . Rhus , p. 131 



153. Bud-scales several. , . Morus, p. 87 



154. Buds glossy-varnished; pith angled. , . Liquid ambar , p. 103 



154. Not as above. 155 



155. Lowest scale of lateral buds centrally located over the leaf- 

 scar; pith angled. . . Populus, p. 55 



155. Not as above. 156 



156. Low shrub with leaves persistent until late in winter, fern- 

 like. ,. Com^tonia, p. 61 



156. Not as above. 157 



157. With resin glands or blisters in sheltered places. 158 



157. Not as above. 159 



158. Stipule-scars elongated; resin in blisters. , . Betula, p. 68 



158, Stipule-scars minute or none. , . Myrica, p. 58 



159. Buds stalked. 160 



159, Buds not stalked. 164 



160. Buds long and spine-like. , . Fagus, p. 73 



160. Not as above. 161 



161. Leaf-scars 2-ranked, 162 



161. Leaf-scars in more than 2 ranks. 163 



162. Buds yellowish. . , HamamQlis , p. 103 



162. Buds black or brown, only the flower-buds stalked. . , Cercis , p, 129 



