142 ROOTS 



ordinary roots? 12. What climbing plants use secondary roots as 

 tendrils ? 13. Describe the way in which the branches of roots arise. 

 Section 43. 1. By what means do plants grow? 2. What is 

 meristem ? 3. Locate the meristem of roots. 4. Distinguish between 

 primary and secondary growth. 5. Define cambium. 6. Locate 

 the region of elongation of roots. Compare it with the region of 

 elongation of stems. 7. Describe a method of demonstrating the 

 region of elongation in roots. 



A. 8. Describe the curvature of roots. 9. Do plants have a sense 

 of touch ? Compare it with your own. 



B. 10. What are the external factors which affect the direction 

 of root growth? n. What are tropisms? 12. Define phototropism, 

 geotropism, and hydrotropism. 13. State the differences between 

 roots, stems, and leaves as to their tropisms. 14. What is a stimulus ? 

 15. Describe the growth of roots and shoots with the effect of gravity 

 removed. 16. Does water or gravity produce a greater effect on the 

 growth of roots ? How may your answer be proved ? 



C. 17. Describe the root-cap. 18. Describe the root-cap of a 

 screw-pine. What does its development indicate? 19. Define the 

 terms heredity and environment. 



D. 20. Describe root-hairs. 21. What is meant by the word 

 permeable? 22. Whatiscutin? 23. Is there any advantage to the 

 plant in the fact that it must constantly produce new root-hairs ? 

 24. What is the advantage in the close adherence of the hairs to the 

 soil grains ? 25. What advantage in the excretion of carbon dioxide 

 by the root-hairs ? 



E. 26. Describe, making a sketch on the board, the internal struc- 

 ture of roots. 27. What advantage is there in having the xylem and 

 phloem radially arranged in roots ? 



Section 44. 1. Define annual, biennial, and perennial. 2. Give 

 examples of annuals, biennials, and perennials. 3. To which of these 

 classes do the plants most valuable to man belong? Explain your 

 answer by giving examples. 4. Explain the fact that the same plant 

 may be sometimes an annual and sometimes a biennial. Give an 

 example. 5. Does the annual or the perennial habit appear to be 

 more successful in plant life ? State the advantages of each. 



Section 45. 1. Describe the contraction of roots in the dande- 

 lion. 2. What advantages are there in this habit ? 



