 gills completely inclosed and never exposed as in the secotioid form of "Lentinus tigrinus")—note—some mycologists do not consider a species to be secotioid unless it has lost ballistospory.Historically agarics and boletes (which bear their spores on a hymenium of gills or tubes respectively) were classified quite separately from the gasteroid fungi, such as puff-balls and truffles, of which the spores are formed in a large mass enclosed in an outer skin.However, in spite of this apparently very great difference in form, recent mycological research, both at microscopic and molecular level has shown that sometimes species of open mushrooms are much more closely related to particular species of gasteroid fungi than they are to each other.