PLANTS 



331 



them live on the juices of living plants. Those that 

 feed on living plants are called parasites, while those 

 that live on decaying matter are called 

 saprophytes (Figure 291). Other com- 

 mon fungi are molds and yeasts. 



Molds are little plants that grow on 

 many organic substances. To study the 

 growth of mold we have only to moisten 

 some bread and cover it to prevent evap- 

 oration. The mold spores on the bread 

 germinate and produce both root and 

 stem threads, on which black knobs full 

 of ripe spores soon appear. These 

 spores are blown about by currents of 

 air. 



Yeast plants are simply one-celled 

 fungi (Figure 292). They are useful as 

 manufacturers of carbon dioxide, to dew, Caused by a 

 raise bread, and in the fermentation of Parasitic Fungus " 

 grains and fruit juices. In the production of carbon 

 dioxide by yeast plants, sugar is changed to alcohol. 



Another group of the fungi are the bacteria. Some of 

 these are parasitic to man and produce human diseases such 



as typhoid fever, diphtheria, 

 and tuberculosis (Figures 293, 

 294). However, many of the 

 bacteria are very useful (Figure 

 295). They cause milk to sour 

 and enable us to make cheese 



FIG. 292. Growing Yea'st Plants. 



FIG. 291. A Wil- 

 low Attacked by Mil- 



decay of organic matter and so change it that it can 

 be used as food for plants. They attach themselves 

 to the roots of plants and help to produce proper food 



