[britishbryologicalsociety.org.uk] Identification Information: When examining any Philonotis, it is always the mature leaves from the previous season among the stem tomentum that should be selected. Younger leaves higher up on the stem (or anywhere on small, possibly juvenile plants) should be ignored. You will also need to have a compound microscope with good quality optics and illumination to clearly see cell mamillae - basic microscopes usually are not good enough. (link added by Mary Ann Machi)