26 LABORATORY AND FIELD EXERCISES 



d. What is the function of thick-walled cells and fibers in 



plants? What function do they serve in the celery 

 stalk examined above ? Why is a cornstalk hard on 

 the outside ? What makes a bamboo fishing rod so 

 strong ? What is the nature of the covering of hick- 

 ory nuts and other similar nuts ? See Figs. 8, 9 and 

 10 of these exercises. 



e. Summarize the functions of thick-walled cells and vege- 



table fibers in plants, and state some of their important 

 economic uses. 



PROTOPLASM, VACUOLES, AND NUCLEI IN 

 ROOT-TIP CELLS 



1. Study of the text and sections. Read the text concerning 

 the nature of protoplasm, vacuoles, and nuclei. Study 

 these parts of the cell in sections of root tips which 

 have been previously stained and mounted for this pur- 

 pose. Transverse sections of root tips are especially 

 favorable for this first study of cells with protoplasmic 

 contents. 



a. Low-power study. Study the cells immediately beneath 



the outer bounding cell layer. 



(1) Protoplasm and vacuoles. Find cells in different 

 stages of vacuole formation as described in the 

 text and illustrated in Fig. 27. Do you find cells 

 in which vacuoles are just beginning to form ? 

 cells in which the vacuoles are large light spaces 

 surrounding the nucleus ? cells which appear to 

 have a continuous large central vacuole? These 

 may be found in deeper-lying cells of the section. 



b. High-potver study. Select a favorable cell and study 



the following structures with a high power: 



