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 
method'if^rowth by ma y in turn produce buds before they separate, 
budding, a, single In either case, two or more cells are produced 
cells; 0, 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. 
