THE GRO'WTK OF ROOTS AND STEMS. 191 



24. How is the direct! on of a root's growth affected by light? How 

 does a shoot differ from a. root in this respect ? 



25. How is the growth, of a root-tip affected by contact with a hard 

 obstacle ? 



26. How can it be proved! that the root-tip alone is sensitive to the 

 stimuli of gravity, light, etc . ? 



27. In what part of a root does growth in length occur? How can 

 it be proved that the curvatures in response to stimuli (gravity, light, 

 moisture, contact) also occnr in this part ? 



28. Describe the characters of the various regions of a root, starting 

 from the extreme tip. 



29. State all you know about the roots of land-plants, and in par- 

 ticular mention any observ ations you have yourself made on the roots 

 of any plants. 



30. Give an account of the influence of Light, Gravity, and Moisture 

 on the growth of roots. 



31. Describe carefully how you would fit up an experiment which 

 would show clearly the effect of light on the direction of growth of 

 the stem and root of a seedling. State briefly the other effects of light 

 on plants. 



32. What is meant by Geufcropism ? Write a careful account of any 

 three experiments you may Jaave performed in order to investigate the 

 nature of geotropic phenomena in roots. 



33. Write a short account of the distribution of mechanical tissue 

 (stereom) in the stems of plants, illustrating your answer by reference 

 to particular cases. 



34. Very strong solutions of certain salts make plants wither ; very 

 weak solutions of the same salts are recommended for making them 

 grow. How would you determine by experiment how strong and how 

 weak solutions must be to produce these effects ? How do you explain 

 the contradictory results ? 



35. Describe the structure of a young root as seen in transverse 

 section. What peculiarities in its structure are characteristic of the 

 root? 



36. If a leaf or a flower-stalk is removed from the plant and allowed 

 to remain in dry air, it becomes flaccid and can no longer support its 

 own weight. Why is this? Give experiments in support of your 

 explanation. 



37. How would you show whether it is the reaction produced by 

 light, or by gravitation, or by both, that causes a stem to grow 

 upwards and a root to grow downwards ? 



