Answer & Explanation:
The examined tissue could be cortex, due to the fact that it's rigid and does not require oxygen, so metabolic processes, like respiration, are not happening. The cortex, or wood, is dead tissue that no longer develops metabolic processes. It starts growing as the plan also grows, and the cambium tissue is in charge of this process.
The independent variable is the one variable you manipulate in the experiment
The dependent variable (or responding variable) changes as a result of the independent variable
The answer is With precipitation
