I tried one method; applying binder gum several layers, let it dry, detach the gum layer and observe under light microscope to see the images, but feel not accurate enough to get the trichome length.

The method i used as follows: Leaf samples (4cm in length) were kept in 95% ethanol overnight to remove the chlorophyll.Then the completely chorophyll removed leaf samples were washed using distilled water and transfered to 0.05% Toluidine blue solution for 2hrs to stain the trichomes and observed under light microscope.I obtained good pictures and measurement of trichomes using this method.

I have tried the above method with tea (Camellia sinensis). Nicely working. Thank you for sharing your experience.