THE MUTUAL RELATIONS OF ORGANISMS 227 



upon others. The minerals that they absorb from the soil 

 are available for plant life only after the bacteria and other 

 soil organisms have acted upon them, the fertility of the soil 

 depending upon its microscopic life. The autophytes, however, 

 do not need organic food, and in this respect are much more 

 independent than the other two groups. 



2. Saprophytes (Gr. sapros = rotten + phyton = plant). 

 Plants which feed upon the dead bodies of other organisms are 

 saprophytes. The plants usually included under this head 

 are the Fungi* These constitute the scavengers of the world, 

 and may be found everywhere in the soil or in bodies of water, 

 where they consume whatever excretions of animals or plants 

 there may be; or live upon dead roots, leaves, and branches; 

 they live, indeed, upon various dead materials that have been 

 derived either from animal or plant life. Such organisms are 

 almost universally distributed over the earth, and they cause 

 all decay and putrefaction, these two processes being the result 

 of the destruction of organic material by Fungi. This class 

 of organisms is ever at work around us, consuming the bodies 

 of dead animals and plants. 



3. Parasites. Plants which live upon and feed upon other 

 living organisms are parasites. In such cases we call the 

 organism upon which they feed the host. Parasitism is very 

 common among both plants and animals, nearly every species 

 having special parasites feeding upon it. As a rule, the para- 

 sitic plants lack chlorophyll and belong to the group of Fungi. 

 Both saprophytes and parasites are holozoic. 



Animals have similar relations, although in some respects 

 they are more complicated. No animals live a life quite inde- 

 pendent of organic food, like the autophytes, since they 

 lack chlorophyll. The great majority of animals are called 

 free-living, but they feed upon dead organic material (vegetable 

 or animal food), and in this respect resemble saprophytes. 

 Quite a large number of animals also feed upon a living host, 

 and are consequently parasites. 



*Under Furtgi are included bacter.a. 



