Two Places for Roots
At a science museum, visitors can compare two Root Windows exhibits. Each holds eight young bean plants of the same kind and age. In the Soil Bed, roots grow in soil. In the Water Bed, roots hang in water through a mesh support. The roots do not take material from the mesh. Museum scientists collected the following observations during a six-week investigation.
First, the scientists chose matching seedlings. They used extra matching seedlings to estimate each group's starting dry plant mass. Dry mass is the mass left after water has been removed. They did not dry and then regrow the exhibit plants. Next, they placed both groups under identical lamps with the same daily lighting time. Both groups received ordinary room air. Scientists kept both groups supplied with water.
The scientists changed the surroundings of the roots: soil or water. Over six weeks, they added a total of 2 grams of dry mineral nutrients to each group, dissolved in water. Mineral nutrients are substances plants need in small amounts. At the end, scientists collected the whole plants, including their roots. Museum staff dried and weighed them. The graph shows the estimated starting dry plant masses and the measured ending dry plant masses.
The Soil Bed began with 4,000 grams of dry soil, weighed before the mineral nutrients were added. After the plants were removed, the dry soil weighed 3,998 grams. The Water Bed had no soil at any time. Both groups made new stems and leaves during the investigation. Scientists recorded masses, but they did not record the number of leaves on each plant.
A nearby exhibit describes other scientific evidence. Carbon dioxide is a gas in air. Scientists have traced material from carbon dioxide into new plant parts. Water enters plants through their roots. Light supplies energy for growth; light itself is not a material that becomes plant tissue. Visitors must combine this information with the Root Windows results to decide which claims the evidence supports.