Developing spores (conidia)  of Mycogone perniciosa

Mycogone perniciosa causes a disease known as wet bubble of commercial mushrooms.  It looks like a two-celled spore and is often described as such.  However, the spore secedes by the rupture of the hyaline (colourless) penultimate cell which is then dead and the 'real' spore is the thick walled, roughened terminal cell.   So!  Take your pick : one-celled or two-celled.