20 



BACTERIA, YEASTS, AND MOLDS 



like a corn ball (Fig. 8, d), — a resemblance which is very 

 striking in some species when the spores are white. This 

 species of mold, even after producing its fruit, remains 

 white ; but a careful examination shows it to be covered 

 all over with minute white balls just big enough to be 

 seen by the naked eye, but looking very beautiful under 



the microscope 

 (F'ig. 9). Each 

 ball is a mass of 

 scores of spores. 

 Some molds of this 

 last type produce 

 brown spores in- 

 stead of white. 



Of the scores of 

 species of molds 

 each has its own 

 method of produ- 

 cing spores. Each 

 is at first a white, 

 threadlike myce- 

 lium, but each in 

 time shows spots 

 of color. When the color begins to appear it commonly 

 means that the mold is producing spores. The spores 

 are nearly always so small and light as to be blown easily 

 by the wind, and in this way they are carried to and fro. 

 The air in any household is almost sure to be filled with 

 them in greater or less abundance, as can easily be proved 

 by simple experiment. Figs. 14-17 show a variety of com- 

 mon molds, with their methods of forming spores. 



Fio. 9. A colony of Asperi^illus as sliown under 

 the microscope on a black background. 



