190 THE GROWTH OF ROOTS AND STEMS. 



10. Explain the structure, as seen in transverse section, of a twig of 

 any Dicotyledonous tree. 



11. State generally what is the composition of a vascular bundle. 

 Describe the longitudinal course of the vascular bundles in the stem of 

 any Dicotyledon. 



12. What is the cambium ? Explain where you would find it in the 

 stem of a tree, and what is its importance. 



13. What is meant by a "vessel"? What are the differences 

 between the vessels of the wood and those of the bast ? 



14. What is a "growing-point"? What is the difference between 

 the growing-points of stems and those of roots ? 



15. Describe the way in which the stem of a Dicotyledonous tree 

 grows in thickness, and explain how it is that its wood shows annual 

 rings. 



16. The stem of an Oak tree continues to grow in thickness so long 

 as the tree lives, whereas the stem of a palm-tree does not grow any 

 thicker when once formed. Explain the cause of this difference. 



17. Along what tissue does the sap ascend in a stem in its passage 

 from root to leaf ? How would you endeavour to prove by experiment 

 the truth of your statement ? What other movement of liquid sub- 

 stance takes place in plants besides the ascent of the sap, and what is 

 the path of this current ? 



18. Explain as far as you can the way in which water is absorbed 

 from the soil by the roots, and the transpiration current maintained, 

 in the case of trees. 



19. What is meant by sclerenchyma ? Give some account of its 

 mode of occurrence in stems, and show how it is of use to the plant. 



20. Describe the process of secondary thickening as seen in the root 

 of a Dicotyledonous tree. What advantages does this secondary 

 thickening confer on the tree ? 



21. Describe in the case of any seedling you may select how the 

 structure characteristic of the root changes into that met with in the 

 young stem. What do you think is the use of the change to the plant ? 



22. What method, other than watering, would you use to recover 

 a plant, growing in the open, which had become flaccid from loss of 

 water? Give reasons for the method adopted. 



23. Describe accurately an experiment which you have seen in which 

 the i-ate of growth of roots or shoots was measured. Which part of 

 the root grows most rapidly in length, and which part absorbs most 

 water? What advantages do plants gain by the increase of their 

 shoots and roots in length and thickness ? 



