636 General and Applied Biology 



on or in the bodies of other plants. The disease of corn, called corn 

 smut, is due to a parasitic fungus (class Basidiomycetes). The wheat 

 rust is produced by a fungus parasite which also spends part of its life 

 cycle on the common barberry (shrub). All of these illustrate the ways 

 in which the ecologic relationships of these parasites and their hosts are 

 influenced. 



Saprophytes are those organisms which live on dead organic mate- 

 rials. Frequently, saprophytic plants or animals require rather specific 

 types of dead materials for their existence so that their ecology is in- 

 fluenced. 



Predaciousness, although somewhat similar to parasitism, differs in 

 that the "host" is destroyed rather quickly, while in parasitism it may 

 be destroyed only after a long period of time. Cats are predacious on 

 mice and robins on earthworms. In each instance the distribution of 

 each species is influenced by the presence of the other. 



(f) Dissemination and Destruction of Plants or Their Seeds by Ani- 

 mals: Seeds or plants themselves may be widely distributed by insects 

 and other animals by having the seeds carried in the digestive tract, on 

 the external surfaces, or by mud on the feet. Many types of useful 

 and detrimental plants and their seeds are destroyed by animals which 

 eat them for food, use them for making nests, parasitize them, or in 

 some other way interfere with their normal habits. 



(g) Plants Contributing Usable Foods and Oxygen; The ecologic 

 relationship between living plants and living animals is quite well known. 

 It usually results in the green plant giving oxygen and food to animals, 

 while the latter give carbon dioxide and waste materials which are use- 

 ful to the plant. 



(h) Plants Detrimental to Certain Animals: Certain types of plants 

 may be detrimental to animals and in that way aff^ect not only the dis- 

 tribution of the animals but also the distribution of the plants. Detri- 

 mental plants may be classed as either poisonous or predacious. The 

 former may produce poisons which may affect animals and thus influ- 

 ence their distribution. The latter, or predacious plants (Fig. 330), 

 actually capture and destroy animals. Examples of such predacious 

 plants are Venus's-flytrap [Dionaea muscipula) , the sundew [Drosera 

 sp.), various pitcher plants (Sarracenia sp., Nepenthes sp., DarUngtonia 

 sp.), and the bladderwort (Utricularia sp.). In Venus's-flytrap the two 

 halves of each leaf blade have long stout teeth and three sensitive hairs. 



