86 



PHYSIOLOGY. 



there is a direct interchange of food material between the two organisms 

 (lichens, mycorhiza, etc.) Disjunctive symbiosis has reference to an inter 

 life relation without any fixed union between them (example, the relations 

 between flowers and insects, ants and plants, and even in a broad sense the 

 relation between saprophytic plants in reducing organic matter to a con- 

 dition in which it may be used for food by the green plants, and these in 

 turn provide organic matter for the saprophytes to feed upon, etc.). Antag- 

 onistic symbiosis is shown in the relation of parasite to its host, reciprocal 

 symbiosis, or miuualistic symbiosis is shown in those cases where both 

 symbionts derive food as a result of the union (lichens, mycorhiza, etc.). 



3. How Fungi Obtain their Food. 



185. Nutrition of moulds. In our study of mucor, as we have seen, the 



growing or vegetative part 

 of the plant, the mycelium, 

 lies within the substratum, 

 which contains the food 

 materials in solution, and the 

 slender threads are thus 

 bathed on all sides by them. 

 The mycelium absorbs the 

 watery solutions throughout 

 the entire system of ramifica- 

 tions. When the upright 

 fruiting threads are devel- 

 oped they derive the materials 

 for their growth directly from 

 the mycelium with which 

 they are in connection. The 

 moulds which grow on de- 

 caying fruit or on other 

 organic matter derive their 

 nutrient materials in the same 

 way. The portion of the 

 mould which we usually see 

 on the surface of these sub- 

 stances is in general the fruit- 

 ing part. The larger part 

 of the mycelium lies hidden 

 within the subtratum. 



186. Nutrition of para- 



Camation rust on leaf and flower stem. From photo- sitic ^ngi. Certain of the 

 graph. fungi grow on or within the 



higher plants and derive their food materials from them and at their ex- 

 pense. Such a fungus is called a parasite, and there are a large number 



