Gautieria spores as viewed through a microscope at 1000x magnification.
The small tick-marks on the scale are one micron (one thousandth of a
millimeter). On the left are G. monticola spores and on the right are
G. pterosperma spores. The spores of G. pterosperma look exactly like
those of G. monticola until immersed in potassium hydroxide (KOH),
which causes the outer sheath (called a utricle) to puff out. The word
"pterosperma" means "winged seed" in Greek.