About 200 years ago, Jan Baptista van Helmont wondered how growing plants obtained the materials necessary for growth. He planted a tree seedling weighing 5 pounds in a barrel filled with 200 pounds of soil and then watered the tree regularly. After five years, the tree weighed 169 pounds, 3 ounces, and the soil weighed 199 pounds, 14 ounces. Because the tree had gained so much weight and the soil had lost so little, he concluded that the tree had gained all of its additional weight by absorbing the water he had added to the barrel. Of course he was incorrect. What really happened?

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Keeath Magee · Accepted Answer

Final Answer : Let's look at the possibilities. The gain in weight of the tree could reflect the water absorbed through the roots and retained in the plant tissues, but not 168 pounds of it! Furthermore, we know that the water molecules are not going to combine directly with any other molecules in the tree. We now know much more about the reactions of photosynthesis than van Helmont did, so we can conclude that the gain in weight was from the synthesis of carbohydrate (specifically, cellulose) in the chloroplasts of the leaf cells due to photosynthesis.

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