- Barnyard grass, [114]
- Beaked nightshade, [156]
- Beaver poison, [148]
- Beggar-ticks, [163]
- Bermuda grass, [113]
- Berteroa, [133]
- Bidens, [162], [163]
- Biennial wormwood, [162]
- Bindweed, [150]
- Bird's-foot trefoil, [139]
- Bitter buttercup, [131]
- Bitter dock, [122]
- Black-eyed susan, [169]
- Black medick, [139]
- Black mustard, [134]
- Black nightshade, [156]
- Black swallow-wort, [149]
- Bladder campion, [130]
- Bladder Ketmia, [146]
- Bloom-fell, [139]
- Bluefield madder, [159]
- Blue grass, [116]
- Blue grass, Canadian, [116]
- Blue grass, Kentucky, [116]
- Blue Vervain, [153]
- Borage family, [152]
- Boraginaceae, [152]
- Bouncing Bet, [129]
- Broad-leaved Dock, [122]
- Broad-leaved plantain, [159]
- Brome grass, [112]
- Bromus, [111]
- Buckwheat family, [119]
- Buckwheat, wild, [120]
- Bulbous buttercup, [132]
- Bull thistle, [164]
- Burdock, [162]
- Bur-grass, [112]
- Bur-marigold, [162]
- Bur-seed, [152]
- Bursa, [134]
- Buttercup, bitter, creeping, or tall, [131]
- Butter and eggs, [156]
- Camelina, [134]
- Canada thistle, [164]
- Canadian blue grass, [116]
- Capriola, [113]
- Capsella, [134]
- Carduus, [164], [165]
- Carpet-weed, [128]
Car´un-cle, an excrescence or protuberance near the hilum of a seed.
- Caryophyllaceae, [128]
- Cashew family, [145]
- Catch-fly, [129], [130]
- Catmint, [154]
- Catnip, [154]
- Celandine, [132]
- c. m. centimeter, see ruled lines on last page, [183]
- Cenchrus, [112]
- Centaurea, [163]
- Centimeter, see ruled lines on last page, [183]
- Cerastium, [129]
- Chaetochloa, [117]
- Charlock, [133]
- Cheat, [112]
- Cheeses, [146]
- Chelidonium, [132]
- Chenopodiaceae, [124]
- Chenopodium, [124], [125], [126]
- Chess, barren, field, smooth, soft, [111]
- Chickory, [164]
- Chickweed, [129], [131]
- Chrysanthemum, [163]
- Cichorium, [164]
- Cicuta, [148]
- Cinquefoil, silvery, [138], [139]
- Cirsium, [164], [165]
- Claviceps, [110]
- Climbing false buckwheat, [121]
- Clover dodder, [151]
- Cockle, [128]
- Cocklebur, [171]
Co´ma, a tuft of hair on a seed.
- Common chickweed, [131]
- Common milkweed, [149]
- Common speedwell, [157]
- Compositae, [160]
- Composite family, [160]
- Conium, [148]
- Conringia, [135]
- Convolvulaceae, [150]
- Convolvulus, [150]
- Corn camomile, [161]
- Corn gromwell, [153]
- Coronilla, [139]
- Couch grass, [110]
- Cow-cress, [136]
- Crab-grass, [113]-114
- Crassulaceae, [138]
- Creeping buttercup, [132]
- Crepis, [165]
- Cress, cow, [136]
- Crimson clover, [141]
- Crowfoot, [131]
- Crowfoot family, [131]
- Cruciferae, [132]
- Curled Dock, [122]
- Cut-leaved Crane's bill, [142]
- Cuscuta, [150], [151]
- Cycloloma, [126]
- Cynanchum, [149]
- Cynodon, [113]
- Cynoglossum, [152]
- Cyperaceae, [118]
- Cyperus, [118]
- Cypress spurge, [143]
Del´toid, shaped like the Greek letter delta; triangular.