THE GROWTH OF ROOTS AND STEMS. 193 



50. When the trunk of a dicotyledonous tree is cut across, the wood 

 is seen to be disposed in rings. Explain this fact, and indicate its 

 relation to the age of the tree. 



51. Why does a succulent flower-stalk or petiole lose most of its 

 rigidity when cut and in want of water ? Could you produce this 

 condition artificially without exposure to the air? How would you 

 attempt to restore the rigidity of a stalk thus artificially wilted ? Give 

 reasons for your answers. 



52. Describe and explain the changes that may be observed when a 

 turgescent shoot is bisected longitudinally, and when the halves are 

 placed successively in water and in strong salt solution. 



53. The split stalks of cut flowers have been found to become limp 

 in salt solutions containing 32 - 5 grammes of salt per litre, but to 

 become turgid in solutions containing 3 "25 grammes per litre. As- 

 suming these facts and given a quantity of the strong solution, how 

 would you most rapidly prepare a series of solutions of intermediate 

 strengths so as to determine what strength of salt solution would just 

 suffice to cause the freshly split stems to become perceptibly limp ? 



54. Explain why it is easier to split a piece of wood in the direction 

 of the grain than across it. 



55. Give an account of the structure and uses of Lenticels. 



56. Describe and explain as fully as you can the appearance 

 assumed by a tree growing in a position fully exposed to the wind 

 from the sea. 



57. How would you distinguish between (a) a simple leaf and a 

 cladode, (6) a compound leaf and a short branch, (c) a slender under- 

 ground stem and a root ? 



58. What are the chief points on which you would lay emphasis in a 

 lesson on Turgescence ? By what experiments would you illustrate the 



59. Explain fully what is meant by Bark, and state the various 

 ways in which it may be formed. 



60. Describe carefully, with diagrams, five plants which reproduce 

 themselves without the aid of seeds. Distinguish carefully between 

 those cases in which food is stored up and those in which it is not. 

 Point out also at what stage the new individuals become separated 

 from the old. 



61. Describe the anatomical structure of the root of a dicotyledonous 

 plant. Show how it is adapted to its surroundings and to the work 

 which it has to perform, and account for the differences in structure in 

 such roots as tap roots and other fleshy roots, as compared with fibrous 

 roots. 



S. B. 13 



