Clubmoss and Physics experiments

I found Fir Clubmoss on the fells as shown above. I had to look it up and found that there is another rarer type called Alpine Clubmoss which is Lycopodium fastigiatum. I use lycopodium powder in Physics and was interested to find out that the powder is the dry spores of such plants. I have used it in an experiment to try to measure the size of an atom. You sprinkle lycopodium powder onto the surface of water and then add an oil drop, having first measured the diameter of the drop to enable the volume to be calculated. The oil slick is then said to have a very flattened cylindrical shape but with the same volume. If you assume the slick is only a few molecules thick, by measuring the diameter and equating the volumes, you get a ball park figure for molecule size. I've never got it to work because the oil slick has never been a decent circle.