Fact 1: Roots have primary and secondary meristems for growth in length and width.

Fact 2: Rulers are used to measure length.

Given the two facts above, answer the question "The growth in what comes from primary and secondary meristems can be measured with a ruler?" with the following options: 
- bushes
 - years
 - Trees
 - three
 - roots
 - bamboo
 - rings
 - a prism


 

     roots    