Lab: claim a pot with pea plants in it. If your pot has more than 3 plants, cut if back to three by cutting the extra plants off at ground level. Leave one plant fully intact. With a toothpick flag, label it "C" for control.
Cut the apex of the main shoot off of the other two plants just below the uppermost leaf.
On the cut surface of one of the plants, put a rice-grain-sized lump of lanolin. Lavel the plant "L" for detipped+lanolin.
On the other plant place a rice-grained-sized lump of lanolin that has 10^-4M Napthalene acetic acid mixed in it. Label the 3rd plant "A" for detipped +Lanolin with auxin.
Our hypotheses are that cutting the apex will stimulate growth by lateral buds and that auxin will suppress that growth.
Why do we have 2 treatments other than the control? What is the purpose of each?
From your description, it seems like 10^-4M Napthalene acetic acid is an independent variable. The other independent variable seems to be the cutting with the lanolin.
In this way, you can separate the effects of cutting and lanolin from cutting, lanolin and 10^-4M Napthalene acetic acid (auxin?) in contrast to no cutting at all.
I hope this helps. Thanks for asking.