Capability to grow in shade might help pines in the dry forests of Arizona to resist drought. How well do such pines grow in shade? Investigators planted 15 pine seedlings in the greenhouse in ether full light, light reduced to 25% of normal by shade cloth, or light reduced to 5% of normal. At the end of study, they dried the young trees as well as weighted them.
Determine the observational units, the experimental units, the treatments, and the response variable in this experiment?