Structure and Work of Stems 39 



64. The Storage of Reserve Food. Annual plants use 

 their food supplies as fast as formed, in developing the 

 shoots and roots, and, particularly, in forming flowers 

 and fruits. Some plants, like turnips, cabbage, radish, 

 etc., store the surplus food in the stem, leaves or roots 

 during the first season, and use it during the next season 

 to nourish a large crop of seeds. If grown in warm cli- 

 mates, these plants will complete the cycle in one sea- 

 son. In plants that live from year to year (perennials), 

 food is stored up in the stems and roots, to supply the 

 needs of the dormant season, and also to form the new 

 crop of root-hairs, leaves and flowers in the following 

 spring. It is the reserve food in the stems that makes 

 the callus and new roots in cuttings of roses, privet, 

 grape, etc. (See, also, K 159.) 



QUESTIONS 



1. Where is the growing point of the stem? 2. What changes 

 take place as the stem lengthens? 3. What is the difference in the 

 arrangement of wood fibers and water vessels in the corn stalk 

 and in plants with netted- veined leaves? 4. Where is the cambium, 

 and what is its work? 5. How are the wounds on plants healed? 

 6. What is the position and use of the phloem layer? 7. Why are 

 trees girdled? 8. How else may the roots of a tree be starved to 

 death? 9. How may perennial weeds be killed? 10. How may 

 Johnson grass be killed? 11. What are the uses of reserve food? 



