Coleus Transpiration on a Balance

Download coleus.dmw

Arguably DataLogging is best used when experiments are run over a very long or very short period. This classic experiment was run over a weekend when the computer would not otherwise have been used.

Method:

A well watered small coleus plant in a light plastic pot is wrapped in a plastic bag with an elastic band around the stalk which ensures that there can be no water loss by evaporation. The pot is placed on an electronic balance which is then set to zero using the tare button. The experiment should ideally be placed near a window while the weather is warm in the Summer.

Datamass is set to record, you can either use the 'Auto Record' mode or set the recording to run for several days with an appropriate time interval (15 - 30 minutes). In this case the experiment was run between the end of school on Friday and early Monday morning on a very hot June weekend, there was very little water left in the plant or pot when the run was terminated!

Results:

This was recorded back in the early 80's when my software removed the "-" sign, so it gives cumulative water loss. If you want this effect you can use the Datamass:Calculate Command from the Data Menu and multiply all readings by "-1".

Using Datamass's cursor we can determine the rate of loss of water:

Improvements

Since this recording was made, it has become possible to record simultaneously with both balance and sensors. It is entirely feasible to do such a run while recording with light, temperature and humidity sensors. Speaking as an ex-chemistry teacher I hope I am right when I say this should show that light levels are more important than temperature in determining transpiration rates.

If you have done or plan to do such an experiment or series of experiments, let us have the results!