In answer to the question, "when a plant grows. where does the material come from?"?

Jan Baptist van Helmont conducted a rather famous experiment to test this hypothesis. He grew a willow tree in a container with a known m of soil. By knowing the m of the tree before it was planted, and by measuring the m again after five years, he could figure out how much m the tree had gained. In comparison, the soil lost m, but much less than what was gained by the tree. So he figured the m gained by the tree had to mostly come from something else. Without reading the article below, can you hypothesize from where the added mass might have come? HINT: What else besides soil does the tree need to grow?