PLANTS WITHOUT CHLOROPHYLL 



133 



Bread mold ; r, rhizoids ; s, fruiting 

 bodies containing spores. 



The Growth of Bread Mold. — If a piece of moist bread is 

 exposed to the air of the schoolroom, or in your own kitchen for a 

 few minutes and then covered with a glass tumbler and kept in a 

 warm place, in a day or two a fuzzy whitish growth will appear on 

 the surface of the bread. This growth shortly turns black. If we 

 now examine a little piece of the 

 bread with a lens or low-powered 

 microscope, we find a tangled 

 mass of threads (the mycelium) 

 covering the surface of the bread. 

 From this mass of threads pro- 

 ject tiny upright stalks bearing 

 round black bodies, the fruit. 

 Little rootlike structures known 

 as rhizoids dip down into the 

 bread, and absorb food for its 

 threadlike body. The upright 

 threads with the balls at the end contain many tiny bodies 

 called spores. These spores have been formed by the division of 

 the protoplasm making up the fruiting bodies into many separate 

 cells. When grown under favorable conditions, the spores will 

 produce more mycelia, which in turn bear fruiting bodies. 



Physiology of the Growth of Mold. — Molds, in order to grow 

 rapidly, need oxygen, moisture, and moderate heat. They seem 

 to prefer dark, damp places where there is not a free circula- 

 tion of air, for if the bell jar is removed from growing mold 

 for even a short time, the mold wilts. Too great or very little 

 heat will prevent growth and kill everything except the spores. 

 They obtain their food from the material on which they live. 

 This they are able to do by means of digestive enzymes given out 

 by the rootlike parts, by means of which the molds cling to the 

 bread. These digestive enzymes change the starch of the bread to 

 sugar and the protein to a soluble form which will pass by osmosis 

 into cells of the mold. Thus the mold is able to absorb food 

 material. These foods are then used to supply energy and make 

 protoplasm. This seems to be the usual method by which sapro- 

 phytes make use of the materials on which they live. 



