92 



ELEMENTS OF GENERAL SCIENCE 



material that they secure their food. Therefore the mush- 

 room is a saprophyte (fig. 47). 



A great many kinds of parasites and saprophytes exist, 

 and some of them, particularly the parasites, cause great 

 damage to our crops. Some of the bacteria are saprophytes, 

 while others are parasites. The host on which parasitic bacteria 

 live may be either a plant or an animal. 



Fi... 47. A common mushroom a saprophytic plant 

 This mushroom grows upon decaying plant and animal materials 



104. Size and growth of bacteria. Bacteria are the smallest 

 of living things, often measuring not over -5-$^-$-$ inch in 

 diameter. Some kinds are considerably larger than this, while 

 others are much smaller (fig. 48). Only the very highest 

 powers of the microscope will give information about their 

 internal structures, and there is good reason to believe that 

 there are bacteria so very minute that they are quite invisible 

 even with the best microscope. 



