These consist of oval cells which contain granules and frequently vacuoles. They grow by the formation of buds from the cells, which increase in size and then separate from their parents.

Great importance attaches to the sprouting fungi from the part they play in fermentations, as they present in this respect many analogies with the bacteria. The proper yeast fungus has the faculty, in its growth, of splitting up sugar into alcohol and carbonic acid.

The sprouting fungi are essentially saprophytic, very few of them even occurring as occasional parasites, unless we include the fungus of thrush as belonging to this class. The proper yeasts are included in the genus saccharomyces, of which several species are distinguished.

Saccharomyces cerevlsiae or Torula cerevisiaa is the common yeast plant. Saccharomyces ellipsoideus is the fungus concerned in the fermentation of wine and it is found in all sorts of fermenting juices of fruits. Saccharomyces mycorderma is found in the scum which forms on fermenting beer. It used to be supposed that it had to do with the development of acetic acid from alcohol and hence was named the vinegar fungus, but this action is probably produced not by it but by a bacillus.