Answer:
The experimental subjects are pine tree seedlings .
Step-by-step explanation:
The physical entity to which the treatment is assigned at random is known as experimental unit .
The same treatment cannot be received by two experimental units, they have to different treatments. The selection of experimental units plays an important role to determine the p-values in the statistical analysis. The experimental units are divided into different homogeneous groups called blocks.
From the question, the experimental subjects identified are pine tree seedlings.