CHAPTER XVI. 

 NUTRITION OF PARASITES AND SAPROPHYTES. 



209. Definition of a parasite. A parasite is an organism, 

 plant or animal, which lives on or in another living organism at 

 its expense, deriving all or a part of its 

 nourishment from it. The plant or 

 animal on which the parasite lives is 

 called the "host." The parasite derives 

 a part or all of its food from its host, 

 usually inflicting more or less injury 

 upon the host or even causing its death. 

 Parasitic plants are represented in nearly 

 all the great branches of the plant king- 

 dom. There are some among the flower- 

 ing plants, some among the algae, the 

 fungi and bacteria, but by far the greater 

 number are found among the fungi and 

 bacteria. One reason for this is that 

 none of the fungi or of the true bacteria 

 have chlorophyll; therefore, they cannot 

 fix carbon, that is, cannot make their 

 own carbohydrate foods, but are de- 

 pendent on chlorophyll-bearing plants 

 for it. The fungi and bacteria which 

 are parasitic on green plants then obtain 

 their carbohydrates directly from their 

 hosts. Those which are parasitic on 

 animals derive their carbon food from 

 animals, but animals get their carbohydrates directly from green 

 plants, which they eat, or "in the final analysis" from plants or 

 animals which do feed on green plants either dead or alive. 



134 



Fig. 97. 

 A saprophytic fungus (Cre- 



E'dotus) growing on a rotten 

 nb in the forest. 



