Introduction

As discussed by J. Lodder, the term “yeasts” developed historically and really includes a heterogeneous group of microorganisms. H. J. Phaff has reviewed the etymology of “yeast”, and equivalent terms in other languages, and point out the consistent relationship to fermentation. The cell envelope consists of the plasma membrane, the periplasmic space, cell wall, and a slime layer. The cell envelope is thus bounded on the inside by cytoplasm, and on the outside by the medium. The periplasmic space is a region of the cell envelope which is bounded by the plasma membrane and the inner aspect of the cell wall. This space includes invaginations in the plasma membrane and outward excursions into the inner aspect of the cell wall. The cell wall is an integument to the cytoplasm and is that part of the cell envelope which confers mechanical stability and dictates shape. The cell envelope is the interface between the cytoplasm and the medium.