192 THE GROWTH OF ROOTS AND STEMS. 



38. Mention an experiment which shows that organic substance 

 formed in the leaves travels down the stem outside the cambium. 



39. Show, by describing and drawing one example, that the branch 

 of a tree may preserve a record of past seasons in its bark and wood. 



40. Suppose you carefully pull up a young bean seedling, and fasten 

 it by means of a pin through the seed to the edge of a shelf, so that 

 the axis of the plant is in a horizontal position, and then keep the air 

 round the plant saturated or nearly saturated with moisture. How will 

 the plant behave during the next few days? Describe any experi- 

 ments you have made bearing on such occurrences, and state what 

 inferences you would draw from them. 



41. What is meant by osmosis, diffusion, turgor, transpiration ? 

 How is the rigidity of a succulent flower stalk affected by placing it 

 (a) in water, (6) in a strong salt or sugar solution ? How would this 

 treatment affect a living cell ? 



42. Draw from memory, and carefully describe the structure, as 

 seen with the naked eye, of a block of oak (or of any other tree with 

 which you are familiar) cut so as to include both the centre of the 

 tree and the bark. 



43. Describe the young main root of some named plant. Where 

 does most rapid increase in length occur, and how can it be demon- 

 strated? Draw a transverse section taken a little way above the 

 region of most rapid growth. 



44. Draw diagrams of longitudinal sections of a root and of a stem. 

 Include the apex and the characteristic lateral appendages in each 

 case. Minute structures, not readily seen with a hand-lens, need not 

 be represented. 



45. Give a short description of the root-system of a young dicotyle- 

 donous plant. Enumerate the more important functions discharged 

 by roots, and explain how the roots are specially adapted to perform 

 these functions. 



46. The trunk of an Oak tree, when in full leaf, is sawn all round so 

 deeply as to cut through the sap-wood. State and explain the effect 

 of this operation. 



47. Describe the features seen in a cross-section of a piece of wood 

 (e.g. of oak or ash) when examined with a lens. Illustrate your answer 

 by means of a diagram. 



48. Explain the nature and mode of origin of "knots" and of 

 "silver grain " in timber. 



49. What is meant by a Medullary Ray? Where are medullary 

 rays found, and what are their uses ? 



