THK STEM 61 
11. Mention the more important structural differences be- 
tween roots and stems, and, as far as you can, give an explana- 
tion of these differences. 
12. Explain the difference between monopodial and sym- 
podial branching. Describe a few examples of each kind. 
13. What different arrangements of the phloem and xylem 
are to be met with in plants? Illustrate your answer by 
examples. 
14. What secondary changes may take place in the stem of 
dicotyledons ? 
15. Give a diagrammatic sketch of a transverse section of 
the stem of the oak in the third year of growth, labelling the 
various tissues shown. 
