COLLATERAL READLXG 505 



(Chap, XXVI) translocation of nitrogen in this experiment probably took 

 place in the form of organic nitrogenous compounds. 



The results of these experiments indicate that although lateral transloca- 

 tion of nitrogen is relatively slow in intact apple trees that it can be forced 

 by spiral ringing. The effects of spiral ringing upon solute translocation 

 gradually disappear as new conductive tissues develop which are oriented with 

 the axes of the elements parallel to the spiral. 



Discussion Questions 



1. Why does a girdled tree die eventually but not immediately? 



2. Root sprouts develop more often on trees of certain species if they are simply 



cut down than if they are girdled. Explain. 



3. Occasionally a deeply girdled tree has been found to live for many years 



after ringing. What are some possible explanations? 



4. When a woody stem is ringed close to the tip just before bud break the 



tip sometimes dies. This is often ascribed to injury to the xylem. Is any 

 other explanation possible? 



5. How would you determine from how far back in the stem system of a tree 



the food used by terminal buds in their spring development comes? 



6. How would you demonstrate whether translocation of foods away from the 



leaves occurs more rapidly in the daytime or at night? 



7. When a woody stem is girdled dormant buds below the girdle often begin 



to develop almost immediately. What explanations can you suggest? 



8. Why does ringing a stem, no matter how carefully it is done, usually de- 



crease the rate of transpiration from leaves attached above the ring? 



9. Pioneers in Indiana made it a rule to girdle trees about August l. Is there 



any scientific justification for this date? 



10. How could you increase the size of a given apple fruit by girdling? How 



decrease it? 



11. Suppose that certain determinations showed that the nitrogen content of 



leaves, expressed as a percentage of their fresh weight, is greater in the 

 daytime than at night. Does this necessarily indicate that nitrogen is 

 translocated out of the leaves at night? 



12. What experimental procedure would you suggest as a more convincing check 



of the interpretation given in question 1 1 ? 



13. Cut stumps of certain species of trees have sometimes been found to remain 



alive for years after the top of tree has been removed. What are some 

 possible explanations? 



Suggested for Collateral Reading 



Curtis, O. F. The translocation of solutes in plants. AIcGraw-Hill Book Co. 



New York. 1935. 

 Miinch, E. Die Stojjbeiuegungen in der Pflanze. Gustav Fischer. Jena. 



1930. 



