THE GENERAL NATURE OF MOLDS 



33 



The general appearance of molds is well known to every 

 one. At first they are soft, fluffy masses, usually white, 

 though later they may become blue, green, brown, black, 

 or red. They grow upon all sorts of material and, under 

 some conditions, with 

 very great rapidity. 

 A typical mold as it 

 appears to the naked 

 eye is shown in Fig. 2. 

 The molds which are 

 liable to appear on the 

 foods in the household 

 are by no means always 

 alike, though the house- 

 keeper rarely recog- 

 nizes any difference 

 between them. They 

 differ in many respects, 

 — -in the fineness of 

 the threads of which 

 they are made, in the 

 rapidity of their 

 growth, in the mate- 

 rials upon which they 

 grow, and more partic- 

 ularly in color ; for while most are white at first, they show 

 many other colors later. The most common of the house- 

 hold molds is one which at the time of fruiting becomes 

 a bluish-green color, and hence is called the "blue mold," 

 Penicillhim glaucum (see Figs, i and 5). This species 

 is common upon bread and cheese, but it will grow upon 



Fig. I. Two colonies of common mold, 

 Penicillhim^ as shown under the micro- 

 scope on a black background. 



