In an attempt to find the basic architecture underlying the known structures of the basidiospore walls some developmental patterns of the formation and reduction of the wall teguments are described. Spore walls are built from two classes of substances differing in their aspect in the electron microscope: an electron dense material and an electron transparent material. These two classes, by mixing and separation, form two classes of teguments, the eusporium and the myxosporium. The teguments are modified by differentiation and reduction processes. A processus called exogenisation leads from an endospore to a false exospore and eventually to a true exospore. A false exospore is morphologically an endospore but functionally an exospore. The wall of the apophyse contributes to the formation of the spore wall. The external layer becomes the sporothecium, the internal layer contributes to the myxosporium if it gelatinizes or to the eusporium if it does not gelatinize. Total reduction of the true spore wall leads to a replacement of the spore wall by the apophyse wall and thus to a true exospore. Some morphologic observations suggest that the basidiospore is not projected by the basidium, but that it actively jumps off the sterigma.