A while back Harry asked “I am particularily interested in the simple stomata experiment. Does anyone have any experience with it and roses?” and the conversation went in a direction of how to calibrate a microscope.
A paper I just found in American Journal of Botany 93(3) 412-425 by S. Joly et al titled “Polyploidy and hybridization in roses east of the Rocky Mountains” does include measurement of stomatal guard cells to differentiate between diploid and tetraploid individuals within a single indigenous american rose specie.
It also references Lewis’s dissertation’s publication which detailed how the test was done and summarizes his methodology.
Once I have leaves again, I’ll do a quick test on my Europeana and its sport. With this measure, I’ll use a micrometer eyepiece at a specific magnification. What the real distance between two black lines is …won’t matter. I’ll just assign a letter to it (or name it for a cat) and do the measurements. As long as I keep the zoom magnification the same, a tick mark on the scope, the measurements will be comparable.
Google search also lists a lot of papers for other genera that use this method of determining ploidy.