86 



PHYSIOLOGY. 



there is a direct intercliange of food material lictn-cen the two organisms 

 (licliens, m^'coi-hiza, etc.) Pisjiindii'e symbiosis lias reference to an inter 

 life relation without any fixed union betA^een 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 \\'hich it may he used for food by the green plants, and these in 

 turn provide organic matter for the sapro]>h}'tes to feed upon, etc.). Avtag- 

 onhtir s\'nibiosis is showai in the relation of jjarasite to its host, reciprocal 

 svmliiosis, or miiiualistic s\'mbiosis is sho\\'n in those cases ^^■here both 

 svmfjionts derive food as a result of the union (lichens, lu^'corhiza, etc.). 



3. How Fungi Obtain their Food. 



185. Nutrition of moulds. — In our stud\' of mucor, as ^^"e Iiave seen, the 



growing or vegetative part 

 of the plant, the m^-celium, 

 lies \^'ithin the substratum, 

 which contains the food 

 materials in solutioUj and the 

 slender threads are thus 

 bathed on all sides by them. 

 The ni}"celium absorbs the 

 watery solutions throughout 

 the entire system of ramifica- 

 tions. AVheii the upright 

 fruiting threads are devel- 

 oped they deri\'e the materials 

 for their growth directly from 

 the mycelium with which 

 they are in connection. The 

 moulds which grow on de- 

 caj-ing fruit or on other 

 organic matter deri\c their 

 nutrient materials in the same 

 wa}-. The porticm lA the 

 mould which we usuall}' see 

 on the surface of these sub- 

 stance's i- in general the fruit- 

 ing part. The larger part 

 of the mycelium lies hidden 

 within the subtratum. 



186. Nutrition of para- 



Fig. 7=;. ^ 



Carnation rust on l«f and floevc-stem. From photo- ^''1" fungi.- Certain of the 



graph. fungi grow on or within the 



liiglier plants and tlerive their food materials from them and at their ex- 

 pense. Such a fungus is called a ^(?/-<«//c, and there area large numfiei 



