The veiled species of Hebeloma in the western United States / Alexander H. Smith, Vera Stucky Evenson, and Duane H. Mitchel.

Plates 9-14 showing spore surface configuration as illustrated
with the aid of the scanning electron microscope. As can be seen in the
illustrations, the details of the spore ornamentation, as seen with aid of
the SEM (on the species studied to date), show a pattern of low
profile.
An oversimplistic explanation of the formation of the ornamentation of the spores, on the species illustrated, suggests that the ornamentation is produced by a thin more or less viscous "ectoperisporial
layer" which becomes pulled apart into the pattern shown, or the layer
is gradually eroded in part by enzyme action. Further studies, obviously, are necessary.