OUR COMMON MOULDS. 



399 



One of the most essential conditions for the development of these 

 minute fungi is the presence of a good degree of moisture. So well 

 known is this, that to many minds moisture and mould hear to each 

 other nothing less than the relation of cause and effect. A warm at- 

 mosphere is also required. In winter the housewife exercises fewer 

 precautions to keep these intruders from her viands than during the 

 warm summer weather. Besides organic matter, moisture, and 

 warmth, a free access of oxygen must be added as an essential condi- 

 tion for the perfect development of moulds. 



When the season comes and the soil is ready, the farmer knows 

 he must sow the seed, or he cannot hope to reap a harvest. So it is 

 with the moulds : to the conditions for growth there must be added 

 the germs of life, or no mould will be produced. How this sowing is 

 accomplished will be better seen after some of the species are con- 

 sidered more in detail. 



Our common bread is a substance which offers special inducements 

 for the growth of various moulds, and, in order to study them, a slice 

 was taken and placed on a zinc rack on a dinner-plate and covered 

 with a glass bell-jar lined with filtering-paper which dipped into 

 some water in the bottom of the plate, producing thus a moist atmos- 

 phere by the evaporation from its extensive surface. This culture 



Fig. 1. Mould Culture. 



(Fig. 1), placed in a warm room, secured all the important conditions 

 for the production of a crop of mould. On the bread thus situated a 

 mould made its appearance in about thirty-six hours, and proved to 

 be one of the most common of the bread-moulds (3Iucor stolonifer), 

 shown in Fig. 2. When first noticeable, the surface of the bread is 

 covered with a cobweb-like mass of fine white threads, called myce- 

 lium, which run in all directions through the tissue of the bread, and 

 perform the work of absorbing nourishment. Soon other and larger 

 threads begin to rise into the air, their tips enlarge, the protoplasmic 

 contents of the threads passing up into the ends, which finally assume 

 a spherical shape. At first these large round heads are of a white 



