THE ROOT AND ITS FUNCTIONS 57 



135. Whicli do you think will tend to have the deeper root-system, 

 a bog plant or a desert plant? Why? 



136. Do you think that a root-systeui will tend to spread further in 

 rich soil or in poor soil? Why? 



137. Roots will usually grow toward a supply of nutrient material in 

 the soil. Can you suggest what causes them to do this? 



138. Root-hairs are entirely absent on the older portions of a root. 

 Why? 



139. Root-hairs are absent from the growing region at the tip of the 

 root. Of what advantage is this fact to the plant? 



140. Of what advantage are root-hairs to the plant aside from their 

 function in the absorption of water and salts? 



141. Root-hairs are commonly absent in water plants. Explain. 



142. The fibro-vascular system of the root is usually in the form of a 

 solid rod, and that of the stem in the form of a hollow tube. Of what 

 advantage to the plant are these arrangements of the tissues? 



143. Why is the soil immediately around the base of a tree trunk 

 somewhat higher than the adjacent soil? 



144. Give an example (other than those cited in the text) of a plant 

 which has a fibrous root-system; a tap-root; climbing roots; parasitic 

 roots. 



145. Why is protoplasm regarded as the only really "living" sub- 

 stance in the plant? 



146. What are some of the ad\-antages of cellular structure in plants 

 and animals? 



147. Give all the reasons you can think of for the fact that cells 

 should be such very small objects. 



148. Why do so many cells have a six-sided appearance? 



149. Of what advantage is the streaming of protoplasm which com- 

 monly takes place in the cell? 



150. What important functions does the cell- wall perform? 



151. Are there any cells of the plant which are useful to the plant 

 after they die? 



152. If a sac made of bladder or a similar osmotic membrane is filled 

 with molasses, tied up, and placed in a vessel of water, what will hai)pen? 



