THE PIN-MOLD FUNGI 495 



algae. The fission fungi, therefore, are regarded as descend- 

 ants of the fission-algaj (as the blue algae are sometimes called) 

 which have adopted a saprophjdic or parasitic mode of life. 

 All plants which contain chlorophyll and, like the algse, 

 make all their own food by means of sunlight, are termed 

 holophytes;^ while those which feed upon organic materials 

 either as saprophytes or parasites are distinguished as hydero- 

 phytcs:' Doubtless in consequence of their change of habit 

 these hysterophytic fission-plants have not only altered their 

 relation to sunlight, but have become more or less reduced 

 in size. Certain species of the group arc, so far as known, 

 the smallest of living things. Multi'plicatlon solely by fission 

 characterizes the class. 



179. The yeast fungi (Class Saccharomycetes). Alco- 

 holic fermentation, or the conversion of a carbohydrate into 

 alcohol and carbonic acid gas, such as takes place in the 

 manufacture of beer and wine and in the raising of bread, 

 is usually accomplished bj' means of yeast. This consists 

 of unicellular fungi (Fig. 151, a-d). The usual method of 

 reproduction differs from fission in that new cells arise as 

 small protuberances or buds which eventually attain the 

 size of the parent cell. Several resting spores are formed 

 in a single cell (e, f) and these germinate by budchng {g, h). 

 There is reason to believe that yeast-plants represent merely 

 a stage in the life-history of more highly developed fungi, 

 which, however, have the i:)ower of perpetuating themselves 

 indefinitely in the simple ways described, much as we have 

 seen to be the case with wall-stain alga. Whatever may prove 

 to be their true relationship to other fungi the species of 

 yeast are conveniently placed provisionally in a class by 

 themselves composed of uvicellidar forms, ivhich reproduce 

 only by budding and the formation of spores by internal cell- 

 division. 



180. The pin-mold fungi (Class Zygomycetes). Various 

 fermentations or putrefactions affecting bread, preserves 

 or other food, are often due to so-called "pin-molds" like 

 the Mucor shown in Figs. 324, 325, 326. A spore falling 



' Hol'o-phyte < Gr. holos, whole; phyton, plant. 

 - Hys'tcr-o-phytc < Gr. hysleros, coming after. 



