The influence of coins on the growth of duckweed

It is well known that copper inhibits the growth of plants, but there are few good materials to demonstrate this fact to students. We used a British one-pence and a Japanese ten-yen coin instead of copper, because they are made mainly of copper. Duckweed serves as on indicator plant, for it could easily be collected and its frond number would increase over a short period, i.e. one or two weeks. The growth could be evaluated by counting the number of fronds. Both coins inhibited the growth of duckweed. Spirodela died in a solution containing a penny after 10 days' culture, and after nine days with a ten-yen coin. The growth curve of Lemna is very similar to Spirodela. From these results, the coin and duckweed investigations were considered to be suitable materials for use in environmental education.