8 THE GENERAL CHARACTERS OF MICROORGANISMS. 



possible to classify them. Frequently only the spore-producing part 

 of the plant is seen, and it may be the only part known, except 

 to botanists. For example, the toad stool is only the reproducing 

 portion of a fungus; it has a mycelium wholly under ground or 

 buried within the hard mass of the trunk of a tree. It is the myce 

 lium, however, that does the work for which these fungi are re 

 sponsible, and not the spore-producing part that we see. Figs, i to 3 

 show the general appearance of some of these fungi and their 

 methods of forming spores. With these methods of reproduction 

 and classification we are not concerned in this work, and only such 

 types as are related to our subject will be mentioned later in their 

 proper places. 



2. Saccharomyces (Yeasts, Budding Fungi) . These immensely 

 important plants are all microscopic in size. While varying 

 somewhat, an average size is, about 1/4000 of an inch in diameter. 

 They are usually spherical or oval in shape, though sometimes 

 slightly elongated (Fig. 4, a). They form no mycelium and cannot 

 force their way into hard substances. Their 

 chief characteristic is their method of reproduc- 

 tion by a process called budding. There appears 

 on the side of the yeast cell a minute bud, which 

 continues to increase in size until it becomes as 

 large as the cell from which it has grown. Then 

 FIG. 4. Yeast the two cells may break apart at once; or each 

 ma 7 in turn produce buds before they separate. 



budding, a, single In either case, two or more cells are produced 



cells; b, budding cells. 



from the one, and although they may remain 

 attached so as to form irregular masses of several cells, (Fig. 4, b), 

 each cell is really complete in itself. Eventually they break apart. 

 This budding takes place rapidly, though not so rapidly as the 

 division of bacteria, which will be mentioned later. 



A second important character of yeasts is the nature of the 

 fermentation they produce. They have an action especially upon 

 sugars, which they break up into carbonic acid and alcohol. This 

 action makes them play a large part in nature's processes, quite 

 distinct from that of bacteria. 



