I reported in my previous post that seventh graders, in three science classes, believed that a tree grows by eating dirt. Historically, that is exactly the belief held up to the Middle Ages.
In 1634 the Belgian Jean Baptist van Helmont performed what may be the first experiment on plant growth. He too hypothesized that a plant grows by somehow absorbing dirt.
To test his theory he devised the following experiment. In an earthen pot containing 200 pounds of soil that had been dried in an oven, he planted a five-pound willow tree shoot. He watered the plant with rainwater and let it grow, watering as necessary.
After the tree had grown for five years, he re-weighed the tree and found that it had grown to 169 pounds. He again dried the soil, weighed it, and found that it still weighed 200 pounds. He concluded that the tree grew by drinking water and not by eating dirt.
In the third and last post in this series I will explain that “eats dirt” may be what science education researcher Dr. Andrea diSessa calls a phenomenological primitive (p-prim). Children, just by living in the physical world, develop their own set of p-prims that may or may not affect their ability to learn school science. The AIMS Center for Math and Science Education is assembling a research team to explore how to help students identify their p-prims. Once identified, students can compare their p-prims with established science and make the necessary adjustments.
Hershey, David R. (1991) Digging Deeper into Helmont’s Famous Willow Tree Experiment. The American Biology Teacher.