124 STEMS 



Make a cross section of a woody stem several years old 

 which grew in a horizontal position. Make a similar sec- 

 tion of a vertical branch from the same plant. Compare 

 the thickness of the rings. How do you account for the 

 difference ? 



111. TWIGS 



Object. Same as in Experiment 110. 



Apparatus. Twigs of ailanthus, beech, ash, or apple. Ailan- 

 thus is preferable on account of its rapid growth and the great size 

 of all its structures. 



Method. Study this twig in the same way. Its large 

 scars and conspicuous lenticels make it particularly good 

 for study. 



Thrust a pin into the topmost bud and fasten a thread 

 to it. Then pass the thread spirally around the twig from 

 bud to bud until it has touched every bud on the stem. 



How many buds at a node? Do you find any trace of a 

 node line? Select any bud and look down the stem until 

 another bud is found directly under it. Now count the 

 number of buds passed over by the thread between these 

 two buds. Also count the number of turns made by the 

 thread in traversing the distance. 



Select any other pair of buds in the same way and count 

 the number of buds and turns of thread as before. 



Is this ratio constant? 



Do the same with beech, oak, ash, apple, or any other 

 tree. Compare them with scales on a pine cone. 



Look for a scar at the extreme end of the ailanthus twig. 



How does it differ from leaf scars, bud scale scars, and 

 fruit scars? What does this terminal scar show? Can 

 you find a terminal bud? Does this plant have definite 

 or indefinite annual growth? Reasons for your answer. 



