X CONTENTS 



PAGE 



§ 21. Tissues 22 



§ 22. Method of study of functions and organs .... 23 



IV. The Roots 



§ 23. Functions of roots 24 



§ 24. Roots hold the stem firmly in position .... 24 



§ 25. Roots were first developed for fixation .... 26 



§ 26. Shrinkage of roots to aid in fixation 27 



§ 27. The structure of the root 28 



§ 28. Climbing roots 28 



§ 29. Stilt roots 29 



§ 30. Columnar roots 29 



§ 31. Keel or ballast roots 30 



§ 32. Substances of which the soil is composed . . . . .30 



§ 33. The soil and root-hairs adhere 31 



§ 34. Root-hairs and the region from which they arise . . 31 



§ 35. Action of roots which have been deprived of hairs . . 32 



§ 36. Can water be taken through the leaves ? . . . .33 



§ 37. The manner in which root-hairs take in liquids . . 34 



§ 38. Action of sugar 35 



§ 39. Another method of imitation of the action of root-haii-s . 35 



§ 40. Action of root-hairs on particles of mineral substance . 36 



§ 41. The fate of the particles of soil 37 



§ 42. Food-material in the soil, and how the plant finds it . 38 

 § 43. The tips of primary or main roots point downward . . 39 

 § 44. The tips of branches of the main roots are directed hori- 

 zontally 39 



§ 45. Sensitiveness of the roots to moisture .... 40 



§ 46. Roots bend away from light 41 



§ 47. The tip of the root is protected by a sheathing cap . . 42 



§ 48. The sensitiveness of roots to touch with solid objects . 43 



§ 49. The roots of air-plants 44 



§ 50. Parasitic roots 45 



§ 51. IMethod of germination and growth of the dodder . . 46 



§ 52. Union of roots with fungi 47 



§ 53. Roots as storage organs 48 



