17. How pigweeds get about . . . . . . . . . . . . . . . . . . . 30 18. Tumbleweeds . . . . . . . . . . . . . . . . . . . . . . . . 31 19. Thin, dry pods, twisted and bent, drift on the snow . . . . 35 20. Seeds found in melting snowdrifts . . . . . . . . . . . . . 36 21. Nuts of the basswood carried on the snow . . . . . . . . . . 37 22. Buttonwood balls . . . . . . . . . . . . . . . . . . . . . . 39 23. Seeds that tempt the wind by spreading their sails . . . . . 40 24. Why are some seeds so small? . . . . . . . . . . . . . . . . 42 25. Seeds with parachutes . . . . . . . . . . . . . . . . . . . 43 26. A study of the dandelion . . . . . . . . . . . . . . . . . . 44 27. How the lily sows its seeds . . . . . . . . . . . . . . . . 46 28. Large pods with small seeds to escape from small holes . . . 47 29. Seeds kept dry by an umbrella growing over them . . . . . . 48 30. Shot off by wind or animal . . . . . . . . . . . . . . . . . 50 31. Seed-like fruits moved about by twisting awns . . . . . . . 51 32. Grains that bore into sheep or dogs or the sand . . . . . . 51 33. Winged fruits and seeds fall with a whirl . . . . . . . . . 52 34. Plants which preserve a portion of their seeds for an emergency . . . . . . . . . . . . . . . . . . . . . . . . 54 CHAPTER VI.--PLANTS THAT SHOOT OFF THEIR SPORES OR SEEDS. 35. Dry pods twist as they split open and throw the seeds . . . 57 36. A seed case that tears itself from its moorings . . . . . . 59 CHAPTER VII.--PLANTS THAT ARE CARRIED BY ANIMALS. 37. Squirrels leave nuts in queer places and plant some of them 61 38. Birds scatter nuts . . . . . . . . . . . . . . . . . . . . . 63 39. Do birds digest all they eat? . . . . . . . . . . . . . . . 64 40. Color, odor, and pleasant taste of fruits are advertisements . . . . . . . . . . . . . . . . . . . . . 65 41. The meddlesome crow lends a hand . . . . . . . . . . . . . . 68 42. Ants distribute some kinds of seeds . . . . . . . . . . . . 69 43. Cattle carry away living plants and seeds . . . . . . . . . 70 44. Water-fowl and muskrats carry seeds in mud . . . . . . . . . 71 45. Why some seeds are sticky . . . . . . . . . . . . . . . . . 72 46. Three devices of Virginia knotweed . . . . . . . . . . . . . 73 47. Hooks rendered harmless till time of need . . . . . . . . . 74 48. Diversity of devices in the rose family for seed sowing . . 76 49. Grouse, fox, and dog carry burs . . . . . . . . . . . . . . 76 50. Seeds enough and to spare . . . . . . . . . . . . . . . . . 78 CHAPTER VIII.--MAN DISPERSES SEEDS AND PLANTS. 51. Burs stick to clothing . . . . . . . . . . . . . . . . . . . 80 52. Man takes plants westward, though a few migrate eastward . . 83 CHAPTER IX.--SOME REASONS FOR PLANT MIGRATION.