THE STEM AND ITS FUNCTIONS 113 



336. Does the trunk of a tree become relatively stouter or more 

 slender, compared with the rest of the tree, as the tree grows larger? 

 Explain. 



337. What difference in method of stem-growth is responsible for the 

 differences in shape between a spruce tree and an elm tree? 



338. A group of trees of the same species, growing very close together, 

 will often have approximately the same shape as that of a single, well 

 developed tree. Explain. 



339. What advantages and what disadvantages does a climbing plant 

 have as compared with an erect one? 



340. What advantages and what disadvantages does a plant with a 

 prostrate stem have as compared with an erect one? 



341. What advantages and what disadvantages does an herbaceous 

 plant have as compared with a tree? 



342. Trees and shrubs have hard and woody stems, but herbs very 

 much softer ones. Explain. 



343. The stems of submersed water plants are very soft and weak. 

 Explain. 



344. Give an example of a plant which is practically stemless. 



345. By looking at a leafy branch which has been freshly cut from a 

 tree, how can you tell whether it has been growing in a vertical, oblique 

 or horizontal position there? 



346. What do you think is the most important function performed 

 by the bud-scales? Explain. 



347. Do all the buds on a tree unfold and grow every season? 

 Explain. 



348. Why is a potato tuber "morphologically" a stem? 



349. Why is it that a woody twig obtains air for its internal tissues 

 through lenticels rather than through stomata, as does a leaf? 



350. What is there about the structure of cork which makes it such 

 excellent material for bottle stoppers? 



351. What do we mean in saying that the cortex and pith are 

 "undifferentiated" tissues? 



352. What is the advantage in having the cells of the conducting 

 tissues much elongated? 



