| 1a. Trees, with erect stem and central trunk, attaining a height of 6 m. (20 ft.) or more — 2. | |
| 1b. Shrubs or woody vines, without true tree habit, or attaining heights of less than 6 m. (20 ft.) — 52. | |
| 2a. Key for use in earliest spring, for trees which have flowers but no leaves — 3. | |
| 2b. Key for use with trees bearing leaves — 21. | |
| 3a. Flowers in catkins, without brightly colored or petal-like parts — 4. | |
| 3b. Flowers not in catkins, either with or without petals — 14. | |
| 4a. Leaf-scars and lateral buds 2-ranked, i. e., in two longitudinal rows with the third leaf above the first — 5. | |
| 4b. Leaf-scars and buds in three or more longitudinal rows — 9. | |
| 5a. From 1 to 3 bud-scales visible on each leaf-bud | 2b, in FAGACEAE, p. 22. |
| 5b. From 4 to 7 bud-scales visible on each leaf-bud — 6. | |
| 5c. From 8 to 20 bud-scales visible on each leaf-bud; buds long and slender; bark of the trunk smooth — 8. | |
| 6a. Bundle-scars 5 or more | 2b, in URTICACEAE, p. 23. |
| 6b. Bundle-scars 3 — 7. | |
| 7a. Twigs bearing numerous dwarf branches thickly covered with crowded leaf-scars (Birch) | BETULACEAE, p. 21. |
| 7b. Twigs without dwarf branches (Ironwood) | 9a, in BETULACEAE, p. 22. |
| 8a. Trunk cylindrical or nearly so | 2a, in FAGACEAE, p. 22. |
| 8b. Trunk prominently fluted with longitudinal ridges | 1b, in BETULACEAE, p. 21. |
| 9a. Bundle-scars 3 in each leaf-scar — 10. | |
| 9b. Bundle scars more than 3 in each leaf-scar — 12. | |
| 10a. Pith divided into separate cavities by transverse partitions | 1a, in JUGLANDACEAE, p. 21. |
| 10b. Pith not partitioned — 11. | |
| 11a. Buds small, with only one external bud-scale | 1b, in SALICACEAE, p. 19. |
| 11b. Buds with more than one outer bud-scale | 1a, in SALICACEAE, p. 19. |
| 12a. Buds clustered near the tips of the twigs | 1b, in FAGACEAE, p. 22. |
| 12b. Buds not clustered at the tips of the twigs — 13. | |
| 13a. Buds with about 3 visible bud-scales | 2b, in FAGACEAE, p. 22. |
| 13b. Terminal bud large, with 4 or more visible bud-scales | 1b, in JUGLANDACEAE, p. 21. |
| 14a. Flowers conspicuous, brightly colored, at least 8 mm. wide. with both calyx and corolla — 15. | |
| 14b. Flowers inconspicuous, seldom brightly colored, and then less than 8 mm. wide — 17. | |
| 15a. Flowers irregular, pink or red | 3a, in LEGUMINOSAE, p. 58. |
| 15b. Flowers regular, white — 16. | |
| 16a. Ovary one, superior, in the center of the flower | 32b, in ROSACEAE, p. 54. |
| 16b. Ovary inferior, appearing as a swelling below the calyx at the summit of the pedicel | 42b, in ROSACEAE, p. 55. |
| 17a. Leaf-scars and buds opposite — 18. | |
| 17b. Leaf-scars and buds alternate — 19. | |
| 18a. Bundle-scar one in each leaf-scar | 1b, in OLEACAE, p. 88. |
| 18b. Bundle-scars 3 or more in each leaf-scar | ACERACEAE, p. 70. |
| 19a. Bundle-scar 1 in each leaf-scar | 1b, in LAURACEAE, p. 41. |
| 19b. Bundle-scars 3 in each leaf-scar — 20. | |
| 19c. Bundle-scars 5 in each leaf-scar | 7a, in LEGUMINOSAE, p. 58. |
| 20a. Branches thorny | 5a, in LEGUMINOSAE, p. 58. |
| 20b. Branches not thorny | 3a, in URTICACEAE, p. 24. |
| — 21— |
| 21a. Leaves narrow, needle-like or scale-like; trees mostly evergreen | PINACEAE, p. 1. |
| 21b. Leaves broader, flat, never needle-like or scale-like, falling in winter — 22. | |
| 22a. Leaves compound — 23. | |
| 22b. Leaves simple — 29. | |
| 23a. Leaves opposite — 24. | |
| 23b. Leaves alternate — 26. | |
| 24a. Leaves palmately compound with 5-7 leaflets | SAPINDACEAE, p. 70. |
| 24b. Leaves pinnately compound — 25. | |
| 25a. Leaflets 3-5 | 1a, in ACERACEAE, p. 70. |
| 25b. Leaflets 7-11 | 1b, in OLEACEAE, p. 88. |
| 26a. Stem or branches thorny | 4a, in LEGUMINOSAE, p. 58. |
| 26b. Stem or branches not thorny — 27. | |
| 27a. Leaflets entire | 7a, in LEGUMINOSAE, p. 58. |
| 27b. Leaflets entire except for a few large glandular teeth near their base | SIMARUBACEAE, p. 65. |
| 27c. Leaflets serrate their entire length — 28. | |
| 28a. Upper leaflets less than 25 mm. wide | 4b, in ROSACEAE, p. 51. |
| 28b. Upper leaflets more than 25 mm. wide | JUGLANDACEAE, p. 21. |
| 29a. Leaves opposite — 30. | |
| 29b. Leaves alternate — 32. | |
| 30a. Leaves entire | CORNACEAE, p. 83. |
| 30b. Leaves toothed or lobed, not entire — 31. | |
| 31a. Leaves lobed | 1b, in ACERACEAE, p. 70. |
| 31b. Leaves merely toothed | 27b, in CAPRIFOLIACEAE, p. 111. |
| 32a. Leaves entire — 33. | |
| 32b. Leaves toothed — 36. | |
| 32c. Leaves lobed — 47. | |
| 33a. Leaves heart-shape | 3a, in LEGUMINOSAE, p. 58. |
| 33b. Leaves not heart-shape — 34. | |
| 34a. Twigs and foliage spicy-aromatic | 1b, in LAURACEAE, p. 41. |
| 34b. Twigs and foliage not aromatic — 35. | |
| 35a. Pith 5-angled; fruit an acorn | 3a, in FAGACEAE, p. 22. |
| 35b. Pith not 5-angled; fruit a berry | 1a, in CORNACEAE, p. 83. |
| 36a. Leaves oblique at base, i. e., one side of the leaf larger than the other — 37. | |
| 36b. Leaves symmetrical, not oblique at base — 38. | |
| 37a. Leaves heart-shape, about as broad as long | TILIACEAE, p. 72. |
| 37b. Leaves oval or ovate, much longer than wide | 1a, in URTICACEAE, p. 23. |
| 38a. Stems thorny | 41b, in ROSACEAE, p. 54. |
| 38b. Stems not thorny — 39. | |
| 39a. Leaves finely toothed, with 3-many teeth per centimeter of margin — 40. | |
| 39b. Leaves coarsely toothed, with 1-2 teeth per centimeter of margin — 46. | |
| 40a. Petioles laterally compressed | 2a, in SALICACEAE, p. 19. |
| 40b. Petioles not compressed — 41. | |
| 41a. Leaves, or many of them, crowded on short spur-like branches — 42. | |
| 41b. Leaves scattered, not on short spur-like branches — 43. | |
| 42a. Bark of the trunks separating in thin papery or leathery sheets | BETULACEAE, p. 21. |
| 42b. Bark of the trunk not papery or leathery | 24b, in ROSACEAE, p. 53. |
| 43a. Lateral leaf-veins straight and parallel, and terminating in the teeth | BETULACEAE, p. 21. |
| 43b. Lateral veins more or less curved, and not ending in the teeth — 44. | |
| 44a. Leaves palmately veined, about as broad as long; juice somewhat milky | 2b, in URTICACEAE, p. 23. |
| 44b. Leaves pinnately veined; juice not milky — 45. | |
| 45a. Willows, with slender leaves and brittle twigs | 8a, in SALICACEAE, p. 19. |
| 45b. Trees with lanceolate, ovate, or oblong leaves and tough twigs | 30, in ROSACEAE, p. 54. |
| 45c. Cottonwoods, with broad, heart-shape or rounded leaves | 1a, in SALICACEAE, p. 19. |
| 46a. Petioles laterally compressed | 2a, in SALICACEAE, p. 19. |
| 46b. Petioles not compressed; lateral veins straight and parallel, running directly to the teeth | FAGACEAE, p. 22. |
| 47a. Stem thorny | 41b, in ROSACEAE, p. 54. |
| 47b. Stem not thorny — 48. | |
| 48a. Leaves palmately veined — 49. | |
| 48b. Leaves pinnately veined — 51. | |
| 49a. Lobes of the leaf entire | 1b, in LAURACEAE, p. 41. |
| 49b. Lobes of the leaf serrate — 50. | |
| 50a.Juice somewhat milky; lateral buds visible | 2b, in URTICACEAE, p. 23. |
| 50b.Juice not milky; lateral buds covered by the base of the petiole | PLATANACEAE, p. 51. |
| 51a. Leaves with 4 large entire lobes; stem marked with a ring at each node | MAGNOLIACEAE, p. 40. |
| 51b. Leaves with many lobes; stem not ringed | 1b, in FAGACEAE, p. 22. |
| — 52— |
| 52a.For specimens bearing leaves only — 53. | |
| 52b. For specimens bearing flowers only — 140. | |
| 52c.For specimens with both leaves and flowers — 155. | |
| 53a. Leaves narrow, needle-like or scale-like, mostly evergreen — 54. | |
| 53b. Leaves broader, flat or rolled, but not needle-like or scale-like — 56. | |
| 54a. Foliage densely gray-pubescent; low bushy shrubs with yellow flowers | 2a, in CISTACEAE, p. 74. |
| 54b.Foliage green — 55. | |
| 55a. Leaves opposite or whorled | PINACEAE, p. 1. |
| 55b. Leaves scattered on the stem | TAXACEAE, p. 2. |
| 56a.Twining or climbing vines — 57. | |
| 56b. Not climbing or twining — 66. | |
| 57a. Thorny vines — 58. | |
| 57b. Not thorny — 60. | |
| 58a.Climbing by tendrils at the base of the leaves | 4b, in LILIACEAE, p. 11. |
| 58b.Tendrils none — 59. | |
| 59a. Leaves simple | 5a, in SOLANACEAE, p. 100. |
| 59b. Leaves compound | 8a, in ROSACEAE, p. 52. |
| 60a.Leaves compound — 61. | |
| 60b.Leaves simple — 63. | |
| 61a. Leaves with 5 leaflets | 1a, in VITACEAE, p. 71. |
| 61b. Leaves with 3 leaflets — 62. | |
| 62a. Plant climbing by tendril-like leaf-stalks | 1a, in RANUNCULACEAE, p. 35. |
| 62b. Plant climbing by hold-fast roots | 5b, in ANACARDIACEAE, p. 69. |
| 63a. Leaves opposite | 5a, in CAPRIFOLIACEAE, p. 110. |
| 63b. Leaves alternate — 64. | |
| 64a. Plants climbing by tendrils | 1b, in VITACEAE, p. 71. |
| 64b. Twining plants — 65. | |
| 65a. Leaves ovate-oblong, attached by the base | 1a, in CELASTRACEAE, p. 69. |
| 65b. Leaves almost round, peltate near the edge | MENISPERMACEAE p. 40. |
| 66a. Leaves opposite — 67. | |
| 66b. Leaves alternate — 84. | |
| 67a. Leaves compound — 68. | |
| 67b. Leaves simple — 69. | |
| 68a. Leaflets 3 | STAPHYLEACEAE, p. 69. |
| 68b. Leaflets 7 or more | 1a, in CAPRIFOLIACEAE, p. 109. |
| 69a. Leaves palmately veined, or at least with a pair of prominent lateral veins from the base — 70. | |
| 69b. Leaves pinnately veined — 72. | |
| 70a. Leaves not lobed | 1b, in RHAMNACEAE, p. 71. |
| 70b. Leaves more or less lobed — 71. | |
| 71a. Leaves with stipules | 22a, in CAPRIFOLIACEAE, p. 111. |
| 71b. Leaves without stipules | 2a, in ACERACEAE, p. 70. |
| 72a. Leaves serrate — 73. | |
| 72b. Leaves entire — 77. | |
| 73a. Stem thorny | 1b, in RHAMNACEAE, p. 71. |
| 73b. Stem not thorny — 74. | |
| 74a. Bark of the ripe twigs green | 1b, in CELASTRACEAE, p. 69. |
| 74b. Bark of the ripe twigs brown, reddish, or gray — 75. | |
| 75a. Twigs with a prominent hairy ridge extending downward from the middle of the line connecting the petiole bases | 13a, in CAPRIFOLIACEAE, p. 110. |
| 75b. Twigs without any pubescent ridge — 76. | |
| 76a. Erect shrubs; leaves obviously toothed | 11b, in CAPRIFOLIACEAE, p. 110. |
| 76b. Spreading shrubs; most of the leaves entire, and only here and there some with serrate margins | 18b, in CAPRIFOLIACEAE, p. 110. |
| 77a. Leaves silvery beneath with a dense coating of scales | ELAEAGNACEAE, p. 77. |
| 77b. Leaves green beneath, or somewhat hairy and light-colored — 78. | |
| 78a. Aquatic plant with lanceolate leaves, and stems bending over and into the water | 1a, in LYTHRACEAE, p. 77. |
| 78b. Not truly aquatic, although frequently in wet places — 79. | |
| 79a. Leaves evergreen, as shown by their presence on the older stems | 18a, in ERICACEAE, p. 85. |
| 79b. Leaves deciduous each year — 80. | |
| 80a. Leaves dotted with translucent dots, easily seen when the leaf is held to the light | 1a, in HYPERICACEAE, p. 73. |
| 80b. Leaves not dotted with translucent dots — 81. | |
| 81a. Lateral veins curved forward and running almost parallel to the leaf-margin | CORNACEAE, p. 83. |
| 81b. Lateral veins spreading, and not paralleling the leaf-margin — 82. | |
| 82a. Leaves with stipules | 1a, in RUBIACEAE, p. 108. |
| 82b. Leaves with a prominent ridge connecting them at the base — 83. | |
| 82c. Leaves with neither stipules nor connecting ridges | 1a, in OLEACEAE, p. 88. |
| 83a. Bundle-scar one in each leaf-scar | 18b, in CAPRIFOLIACEAE, p. 110. |
| 83b. Bundle-scars three in each leaf-scar (Honeysuckle) | 12, in CAPRIFOLIACEAE, p. 110. |
| 84a. Leaves compound — 85. | |
| 84b. Leaves simple — 95. | |
| 85a. Stems prickly or thorny — 86. | |
| 85b. Stems without prickles or thorns — 88. | |
| 86a. Leaves twice-pinnate | 1a, in ARALIACEAE, p. 80. |
| 86b. Leaves evenly pinnate | 5b, in LEGUMINOSAE, p. 58. |
| 86c. Leaves odd-pinnate or trifoliate — 87. | |
| 87a. Leaflets entire 1a, | 1a, in RUTACEAE, p. 65. |
| 87b. Leaflets serrate 3b, | 3b, in ROSACEAE, p. 51. |
| 88a. Leaflets 3 — 89. | |
| 88b. Leaflets 5 to many — 91. | |
| 89a. Tall shrubs; leaflets entire or minutely toothed | 1b, in RUTACEAE, p. 65. |
| 89b. Shrubs 2 m. high or less; leaves conspicuously toothed — 90. | |
| 90a. Stipules present | 17b, in ROSACEAE, p. 53. |
| 90b. Stipules none | 1b, in ANACARDIACEAE, p. 68. |
| 91a. Leaflets 6-25 mm. long — 92. | |
| 91b. Leaflets 30 mm. long, or more — 93. | |
| 92a. Leaflets mostly 5, rarely 3 or 7 | 7a, in ROSACEAE, p. 52. |
| 92b. Leaflets mostly 9-19, 15 mm. long or more | 26a, in LEGUMINOSAE, p. 60. |
| 92c. Leaflets mostly 25-45, less than 15 mm. long | 8a, in LEGUMINOSAE, p. 58. |
| 93a. Leaflets entire | 3a, in ANACARDIACEAE, p. 68. |
| 93b. Leaflets entire, except for 1-4 large glandular teeth near their base | SIMARUBACEAE, p. 65. |
| 93c. Leaflets toothed throughout — 94. | |
| 94a. Juice milky | 1a, in ANACARDIACEAE, p. 68. |
| 94b. Juice not milky | 3a, in ROSACEAE, p. 51. |
| 95a. Leaves minute, scale-like, appressed | 2a, in CISTACEAE, p. 74. |
| 95b. Leaves 3-10 mm. long, spreading, completely rolled into a tube | EMPETRACEAE, p. 68. |
| 95c. Leaves normal in shape, green in color — 96. | |
| 96a. Leaves evergreen, as shown by their presence on the older parts of the stem | 4b, in ERICACEAE, p. 84. |
| 96b. Leaves deciduous — 97. | |
| 97a. Stems or branches thorny — 98. | |
| 97b. Stems or branches without thorns or thorny leaves — 103. | |
| 98a. Leaves conspicuously palmately veined — 99. | |
| 98b. Leaves pinnately veined, or sometimes with smaller lateral veins arising from the end of the petiole — 100. | |
| 99a. Leaves 5 cm. wide or less | 1a, in SAXIFRAGACEAE, p. 49. |
| 99b. Leaves 15 cm. wide or more | 1a, in ARALIACEAE, p. 80. |
| 100a. Leaves entire | 5a, in SOLANACEAE, p. 100. |
| 100b. Leaves toothed or somewhat lobed — 101. | |
| 101a. Leaves with bristly margins; some of the thorns three-pointed | 2a, in BERBERIDACEAE, p. 40. |
| 101b. Leaves not bristly on the margin; thorns not branched — 102. | |
| 102a. Only lateral thorns present | 41b, in ROSACEAE, p. 54. |
| 102b. Only terminal thorns present | 2a, in RHAMNACEAE, p. 71. |
| 103a. Leaves palmately veined, or with one or more pairs of lateral veins from the base of the leaf — 104. | |
| 103b. Leaves pinnately veined — 111. | |
| 104a. Leaves entire — 105. | |
| 104b. Leaves toothed — 106. | |
| 104c. Leaves palmately lobed — 108. | |
| 105a. Foliage fragrant when crushed; leaves ovate | 1b, in LAURACEAE, p. 41. |
| 105b. Foliage not aromatic; leaves heart-shape | 3b, in LEGUMINOSAE, p. 58. |
| 106a. Lateral veins straight and parallel, running to the teeth of the leaf | 3a, in BETULACEAE, p. 22. |
| 106b. Lateral veins curved or branched, and not running straight to the teeth — 107. | |
| 107a. Tall shrubs with somewhat milky juice and broadly ovate leaves | 2b, in URTICACEAE, p. 23. |
| 107b. Low shrubs less than 1 m. high with watery juice | 1b, in RHAMNACEAE, p. 71. |
| 108a. Leaves with 2 or 3 entire lobes, spicy-fragrant when crushed | 1b, in LAURACEAE, p. 41. |
| 108b. Leaves with milky juice | 2b, in URTICACEAE, p. 23. |
| 108c. Leaves neither spicy-fragrant nor with milky juice — 109. | |
| 109a. Stem covered with brown bristles | 29, in ROSACEAE, p. 54. |
| 109b. Stem not bristly — 110. | |
| 110a. Sides of the petiole strongly decurrent on the stem; bundle-scars crowded or nearly in contact in the leaf-scars | 28b, in ROSACEAE, p. 53. |
| 110b. Sides of petiole little decurrent or not at all; bundle-scars distinctly separate | 2b, in SAXIFRAGACEAE, p. 49. |
| 111a. Leaves aromatically fragrant when crushed — 112. | |
| 111b. Leaves not aromatically fragrant when crushed — 113. | |
| 112a. Leaves broadly obovate, entire; a common woodland shrub | 1a, in LAURACEAE, p. 41. |
| 112b. Leaves linear-lanceolate or oblanceolate, conspicuously toothed or entire | MYRICACEAE, p. 20. |
| 113a. Leaves entire — 114. | |
| 113b. Leaves toothed or lobed — 121. | |
| 114a. Base of the petiole covering the axillary buds; twigs marked with rings | THYMELAEACEAE, p. 77. |
| 114b. Base of petiole not covering the bud, and twigs not marked with rings — 115. | |
| 115a. Pith with prominent partitions; tall shrubs with fetid bark; leaves obovate, 10 cm. long or larger | ANONACEAE, p. 40. |
| 115b. Pith not partitioned; leaves smaller — 116. | |
| 116a. Leaves waxy or resinous underneath | 24b, in ERICACEAE, p. 86. |
| 116b. Leaves not waxy or resinous — 117. | |
| 117a. Lateral veins curved forward and almost parallel to the margin of the leaf | 2a, in CORNACEAE, p. 83. |
| 117b. Lateral veins spreading — 118. | |
| 118a. Leaves lanceolate or linear, much longer than wide — 119. | |
| 118b. Leaves ovate or elliptical — 120. | |
| 119a. Stem weak, spreading or trailing | 5a, in SOLANACEAE, p. 100. |
| 119b. Stems, or some of them, erect | 3b, in LEGUMINOSAE, p. 58. |
| 120a. Leaves with purple petioles, which are at least one-fourth as long as the leaf-blade | 1a, in AQUIFOLIACEAE, p. 69. |
| 120b. Leaves with short petioles or sessile | 24c, in ERICACEAE, p. 86. |
| 121a. Lateral veins straight and parallel, mostly ending in the teeth of the leaf — 122. | |
| 121b. Lateral veins not straight and parallel — 129. | |
| 122a. Leaves 2-ranked, i. e., in two longitudinal rows, with the third leaf directly above the first — 123. | |
| 122b. Leaves not 2-ranked — 127. | |
| 123a. Leaves unsymmetrical, oblique at the base, i. e., with one side of the leaf larger than the other | HAMAMELIDACEAE, p. 51. |
| 123b. Leaves symmetrical or nearly so at the base — 124. | |
| 124a. Lateral leaf-veins ending in the leaf-teeth — 125. | |
| 124b. Lateral veins not ending in the teeth | 42b, in ROSACEAE, p. 55. |
| 125a. Bark smooth and fluted on the large stems | 1b, in BETULACEAE, p. 21. |
| 125b. Bark rough or warty or glandular — 126. | |
| 126a. Leaves 4 cm. long or less | 3a, in BETULACEAE, p. 22. |
| 126b. Leaves 5 cm. long or more | 9b, in BETULACEAE, p. 22. |
| 127a. Pith 3-angled | 6a, in BETULACEAE, p. 22. |
| 127b. Pith 5-angled | 13b, in FAGACEAE, p. 23. |
| 127c. Pith cylindrical — 128. | |
| 128a. Leaves finely serrate | 42b, in ROSACEAE, p. 55. |
| 128b. Leaves coarsely or doubly serrate | 41a, in ROSACEAE, p. 54. |
| 129a. Leaves coarsely or doubly serrate — 130. | |
| 129b. Leaves simply serrate — 131. | |
| 130a. Leaves 2-ranked, i. e., in two longitudinal rows, with the third leaf directly over the first | 9b, in BETULACEAE, p. 22. |
| 130b. Leaves not 2-ranked | 41a, in ROSACEAE, p. 54. |
| 131a. Leaves with glands on the petiole or at the base of the leaf-blade — 132. | |
| 131b. Leaves with small dark glands on the upper side of the mid-vein | 42a, in ROSACEAE, p. 54. |
| 131c. Leaves without glands — 133. | |
| 132a. Willows; with usually slender leaves, frequently conspicuous broad stipules, and lateral buds protected by a single external bud-scale | 13, in SALICACEAE, p. 20. |
| 132b. Plums and cherries; with leaves lanceolate or broader, and stipules minute and falling early in the season; lateral buds with more than one bud-scale | 30, in ROSACEAE, p. 54. |
| 133a. With stipules or with stipular scars indicating where stipules have been detached — 134. | |
| 133b. Without stipules or stipular scars — 138. | |
| 134a. With three bundle-scars in each leaf-scar — 135. | |
| 134b. With one bundle-scar in each leaf-scar — 136. | |
| 135a. Willows; usually with slender leaves and twigs and frequently with large conspicuous stipules; lateral buds covered by a single external bud-scale | 13, in SALICACEAE, p. 20. |
| 135b. Juneberries; with oblong or ovate leaves and small stipules which fall early; lateral buds with more than one external scale | 42b, in ROSACEAE, p. 55. |
| 136a. Leaves mostly entire, only a few here and there with low teeth | 1a, in AQUIFOLIACEAE, p. 69. |
| 136b. Leaves sharply toothed — 137. | |
| 137a. Axillary buds superposed, i. e., with a second one just above the first | 1b, in AQUIFOLIACEAE, p. 69. |
| 137b. Axillary buds not superposed | 2b, in RHAMNACEAE, p. 71. |
| 138a. Leaves with purple petioles, which are at least one-fourth as long as the blade | 1a, in AQUIFOLIACEAE, p. 69. |
| 138b. Leaves short-petioled or sessile — 139. | |
| 139a. Stems erect and straight, unbranched or with very few branches | 27, in ROSACEAE, p. 53. |
| 139b. Stems more or less crooked and freely branched, making a spreading shrub | 25, in ERICACEAE, p. 86. |
| — 140— |
| 140a. Flowers appearing in autumn, after the leaves have fallen | HAMAMELIDACEAE, p. 51. |
| 140b. Flowers appearing in spring, before the leaves have opened — 141. | |
| 141a. Flowers in catkins, without brightly colored or petal-like parts — 142. | |
| 141b. Flowers not in catkins, either with or without brightly colored or petal-like parts — 149. | |
| 142a. Leaves 2-ranked, as shown by the arrangement of buds and leaf-scars in two longitudinal rows, so that the third bud is directly over the first — 143. | |
| 142b. Leaves and leaf-scars not 2-ranked — 146. | |
| 143a. Bundle-scars three in each leaf-scar — 144. | |
| 143b. Bundle-scars several in each leaf-scar | 2b, in URTICACEAE, p. 23. |
| 144a. Leaf-buds with only 1-3 visible bud-scales | 10, in BETULACEAE, p. 22. |
| 144b. Leaf-buds with more than 3 visible scales — 145. | |
| 145a. Bark of the branches smooth and dark gray, the larger stems fluted with projecting longitudinal ridges | 1b, in BETULACEAE, p. 21. |
| 145b. Branches without projecting ridges | 4, in BETULACEAE, p. 22. |
| 146a. Pith 3-angled | 8, in BETULACEAE, p. 22. |
| 146b. Pith 5-angled | 13b, in FAGACEAE, p. 23. |
| 146c. Pith cylindrical — 147. | |
| 147a. Visible outer bud-scales 2 or more — 148. | |
| 147b. Buds with a single visible outer scale | 13, in SALICACEAE, p. 20. |
| 148a. Bundle-scars 3 in each leaf-scar | MYRICACEAE, p. 20. |
| 148b. Bundle-scars more than 3 in each leaf-scar | 2b, in URTICACEAE, p. 23. |
| 149a. Flowers dark red-purple, about 3 cm. wide | ANONACEAE, p. 40. |
| 149b. Flowers bright pink, irregular, about 1 cm. wide | 3a, in LEGUMINOSAE, p. 58. |
| 149c. Flowers white, with 5 conspicuous petals — 150. | |
| 149d. Flowers greenish or yellowish, small, inconspicuous — 152. | |
| 150a. Ovary 1, superior, i. e., in the center of the flower and not attached to surrounding parts | 36, in ROSACEAE, p. 54. |
| 150b. Ovary inferior, appearing as a swelling below the calyx at the apex of the pedicel — 151. | |
| 151a. Flowers in racemes or solitary | 42b, in ROSACEAE, p. 55. |
| 151b. Flowers in flattened or rounded branching clusters | 42a, in ROSACEAE, p. 55. |
| 152a. Stems thorny | 1a, in RUTACEAE, p. 65. |
| 152b. Stems not thorny — 153. | |
| 153a. Bark pleasantly aromatic when crushed; perianth with 6 parts — 154. | |
| 153b. Bark not pleasantly aromatic; perianth with 4 short lobes | THYMELAEACEAE, p. 77. |
| 154a. Flowers in sessile lateral clusters | 1a, in LAURACEAE, p. 41. |
| 154b. Flowers in peduncled terminal clusters | 1b, in LAURACEAE, p. 41. |
| — 155— |
| 155a. Leaves narrow, needle-like or scale-like, mostly evergreen — 54. | |
| 155b. Leaves broader, flat or rolled, but not needle-like or scale-like — 156. | |
| 156a. Twining or climbing vines — 56. | |
| 156b. Not twining or climbing — 157. | |
| 157a. Leaves opposite — 158. | |
| 157b. Leaves alternate — 165. | |
| 158a. Leaves compound — 68. | |
| 158b. Leaves simple — 159. | |
| 159a. Leaves broad, palmately lobed — 160. | |
| 159b. Leaves not palmately lobed — 161. | |
| 160a. Flowers greenish-yellow, in racemes or panicles | 2a, in ACERACEAE, p. 70. |
| 160b. Flowers white, in rounded or flattened clusters | 22a, in CAPRIFOLIACEAE, p. 111. |
| 161a. Flowers in close clusters, subtended by four large white petal-like bracts | 4b, in CORNACEAE, p. 83. |
| 161b. Flowers small, white, in dense spherical heads | 1a, in RUBIACEAE, p. 108. |
| 161c. Flowers not in dense heads, and not subtended by petal-like bracts — 162. | |
| 162a. Petals separate from each other — 163. | |
| 162b. Petals united with each other — 164. | |
| 163a. Flowers dark purple-red | 1b, in CELASTRACEAE. p. 69. |
| 163b. Flowers bright yellow | 1a, in HYPERICACEAE, p. 73. |
| 163c. Flowers pink-purple; aquatic shrubs | 1a, in LYTHRACEAE, p. 77. |
| 163d. Flowers white | 5, in CORNACEAE, p. 83. |
| 163e. Flowers minute, greenish; twigs usually thorny | 1b, in RHAMNACEAE, p. 71. |
| 163f. Flowers small, yellowish; leaves silvery beneath | ELAEAGNACEAE, p. 77. |
| 164a. Stamens 2 | 1a, in OLEACEAE, p. 88. |
| 164b. Stamens 4 or 5 | 11, in CAPRIFOLIACEAE, p. 110. |
| 164c. Stamens 10 | 18a, in ERICACEAE, p. 85. |
| 165a. Leaves once-compound — 166. | |
| 165b. Leaves simple — 172. | |
| 165c. Leaves twice- or thrice-compound | 4a, in ARALIACEAE, p. 80. |
| 166a. Flowers small, greenish or greenish-yellow — 167. | |
| 166b. Flowers conspicuous, white, or brightly colored — 170. | |
| 167a. Stems thorny | 1a, in RUTACEAE, p. 65. |
| 167b. Stems not thorny — 168. | |
| 168a. Leaflets 3, entire or minutely toothed | 1b, in RUTACEAE, p. 65. |
| 168b. Leaflets 3, conspicuously toothed | 1b, in ANACARDIACEAE, p. 68. |
| 168c. Leaflets more than 3 — 169. | |
| 169a. Leaflets entire except for 1-4 large glandular teeth near their base | SIMARUBACEAE, p. 65. |
| 169b. Leaflets entire, or toothed for their entire length | ANACARDIACEAE, p. 68. |
| 170a. Flowers with a single bright-blue petal | 8a, in LEGUMINOSAE, p. 58. |
| 170b. Flowers with several petals — 171. | |
| 171a. Flowers regular | 3, in ROSACEAE, p. 51. |
| 171b. Flowers irregular, the upper petal the largest | 4, in LEGUMINOSAE, p. 58. |
| 172a. Leaves minute, scale-like, appressed | 2a, in CISTACEAE, p. 74. |
| 172b. Leaves 3-10 mm. long, spreading, completely rolled into a tube | EMPETRACEAE, p. 68. |
| 172c. Leaves normal in shape, green in color — 173. | |
| 173a. Leaves evergreen, as shown by their presence on the older parts of the stem | 4b, in ERICACEAE, p. 84. |
| 173b. Leaves deciduous — 174. | |
| 174a. Flowers in catkins, without petal-like parts — 142. | |
| 174b. Flowers not in catkins, either with or without petal-like parts — 175. | |
| 175a. Flowers small, inconspicuous, yellowish or greenish in color — 176. | |
| 175b. Flowers white or colored, with conspicuous petals — 180. | |
| 176a. Leaves broad and palmately lobed; stem thorny | 1a, in ARALIACEAE, p. 80. |
| 176b. Leaves entire, toothed, or with 2-3 entire lobes; stem not thorny — 177. | |
| 177a. Flowers in small axillary clusters; foliage not spicy-aromatic — 178. | |
| 177b. Flowers in clusters terminating last year’s twigs; foliage spicy-aromatic | 1b, in LAURACEAE, p. 41. |
| 178a. Petals none; sepals present | 2b, in RHAMNACEAE, p. 71. |
| 178b. Petals present but small — 179. | |
| 179a. A stamen in front of each petal | 2a, in RHAMNACEAE, p. 71. |
| 179b. A stamen between each two petals | AQUIFOLIACEAE, p. 69. |
| 180a. Petals united with each other; stamens 8-10 | 24, in ERICACEAE, p. 86. |
| 180b. Petals separate from each other — 181. | |
| 181a. Petals 4 — 182. | |
| 181b. Petals 5 — 183. | |
| 181c. Petal-like sepals 6; real petals none; foliage spicy-aromatic | 1b, in LAURACEAE, p. 41. |
| 181d. Petals 6; sepals also present — 187. | |
| 182a. Flowers in late spring or early summer | 2a, in CORNACEAE, p. 83. |
| 182b. Flowers in autumn | HAMAMELIDACEAE, p. 51. |
| 183a. Corolla irregular, the upper petal largest | 3b, in LEGUMINOSAE, p. 58. |
| 183b. Corolla regular, all petals alike in size and shape — 184. | |
| 184a. Stamens 5 — 185. | |
| 184b. Stamens 10 or more | 24, in ROSACEAE, p. 53. |
| 185a. Flowers in loose racemes or axillary clusters | 2, in SAXIFRAGACEAE, p. 49. |
| 185b. Flowers in branching clusters — 186. | |
| 186a. Leaves palmately lobed; stem thorny | 1a, in ARALIACEAE, p. 80. |
| 186b. Leaves not lobed; stem not thorny | 1b, in RHAMNACEAE, p. 71. |
| 187a. Flowers dark red-purple | ANONACEAE, p. 40. |
| 187b. Flowers yellow | 2a, in BERBERIDACEAE, p. 40. |