Also, the fertilizer is not basic so as to cause the water molecules to exist as OH - molecules, which would also disrupt hydrogen bonding. A possible confounding variable in this experiment was that we were unaware of the length of time that the twigs had been cut from the trees. Also, the twigs used for the experiment were all brought to into the classroom at the same time. Therefore, the twigs tested later during the period were exposed to the light from the classroom lights as well as from the windows for a longer amount of time than were the twigs tested earlier in the period. Another confounding variable is that stem surface area was not accounted for.
Plants have stomata on both their leaves and their stems.
Thus, twigs with larger stems will transpire more than leaves with smaller stems. The next step in the investigation would be to repeat the experiment with a larger sample size.