Suggestions for Laboratory Work to Precede Chapter Thirteen 



1. Sketch a few twining stems. Note the twist of the stem as, 

 shown by surface markings. 



2. Sketch examples of tendrils. The Boston ivy, gourd, pea, 

 sweet pea, and grape are readily obtainable. Is the spiral con- 

 tinuously coiled in one direction ? Why ? 



3. Dissect a cactus stem. Note the nodes, internal water- 

 storage and food-storage tissue, and green tissue. 



4. Make drawings of a rootstock, corm, bulb, and tuber. Divide 

 each of them into halves by cutting through the longitudinal axis. 

 Compare their advantages as organs of propagation and storage. 



5. Examine stems of water hyacinth, bulrush, and pondweed, 

 noting air chambers. 



6. Examine a cross section of a grapevine or a rattan stem. 

 Note the large size of the water tubes. 



IS3 



