EXERCISE 69 



DOES THE BARK ASSIST IN STRENGTHENING THE STEM? 



Materials. A dozen straight branches of willow, or other available 

 tree, not over one-half inch in diameter, all of the same diameter 

 and as nearly alike in all particulars as possible ; small bucket and 

 sand; balances. 



Directions for work. Select eight or ten of the branches and 

 divide them into two lots. Peel the bark from one lot, but do 

 not injure the remainder. Support one of the sticks across two 

 chairs which are two feet apart. Attach the bucket to the stick 

 midway between the chairs and add sand until the stick breaks 

 or gives way in some manner. Weigh the bucket and sand to 

 determine the force applied at instant of failure, and record the 

 weight below. Do the same with each stick. 



What is the average breaking force for those with bark ? 

 For those without ? Can you determine by examination of the 

 broken sticks how the bark gave strength ? 



[85] 



