An early experiment by van helmont (1600s) describes how he grew a tree in a large pot and found that after five years, the amount of soil in the pot had not changed. he concluded that the increase in weight was due to the addition of water. at that time, the compounds of the air had not yet been identified. today, it is known that he only discovered half the story. which of these experiments would not provide evidence that materials from a source other than water were involved in photosynthesis?