Under very favourable conditions multiplication occurs so rapidly that the daughter-cells themselves commence to form buds, before they have separated from their mother-cell, with the result that pearl-like chains of cells are produced. When the yeast-cells have only limited nutriment, with an abundant supply of air, at a suitable temperature, an endogenous formation of _spores_ takes place. The protoplasm of the cells divides into 1–4 (rarely a greater number) masses (Fig. 182 _c_, _d_, _e_) which surround themselves with a thick cell-wall, and in this state can withstand adverse conditions and periods of dryness lasting for several months. The _sporangia are not asci_ since they have no definite form, and a definite number, form and size of spores is not found. The spores in the different species and kinds occupy varying periods for their development, although exposed to the same temperature, a fact of importance in determining one from another. On germination the wall of the mother-cell is destroyed, and each spore gives rise to a new cell, multiplication taking place by budding (Fig. 182 _f_). The majority of Yeast-Fungi are able to produce alcoholic fermentation in saccharine fluids. The most important of these Fungi is the Beer-yeast (_Saccharomyces cerevisiæ_) with ovate, ellipsoidal or spherical cells (Fig. 182). It is a plant which has been cultivated from time immemorial, on account of its property of producing alcoholic fermentation in sugar-containing extracts (wort), derived from germinating barley (malt). Carbonic acid is also set free during this process. The “surface-yeast” (Fig. 182 _a_), which produces ordinary beer when the brewing takes place at higher temperatures, has cell-chains; “sedimentary yeast” (Fig. 182 _b_), used in the brewing of Bavarian beer, has spherical cells, solitary, or united in pairs. Both these and the following Yeast-Fungi include, according to Hansen, several species and kinds. [Illustration: FIG. 183.--_Saccharomyces mycoderma._]