NUTRITION OF PARASITES AND SAPROPHYTES I 2Q 



etc. It becomes a great pest sometimes in apple orchards, and 



the farmers are said to welcome the collectors who gather it for 



Christmas " greens." 



212. Nutrition of para- 

 sitic fungi. Examples 



of the parasitic fungi are 



the rusts of grains, grasses 



and many other plants; 



the smut of corn, cereals, 



etc., the powdery mildews, 



the downy mildews, etc. 



(See Chapters XXVII and 



XXVIII.) Here it is only 



necessary to describe their 



mode of nutrition. In the 



growing stage these fungi 



produce slender branched 



thread-like structures which 



spread in the form of a mold 



over the surfaces of the 



leaves, or penetrate into the 



tissues of their hosts. The absorption of food substance takes 



place either directly by the threads 

 of the fungus, or the threads de- 

 velop specialized short branches, 

 simple or branched, which penetrate 

 the cell walls and lie in the proto- 

 plasm of the host cell. These 

 special branches are the haustoria. 

 They absorb food substances which 



Cells from tl/sfenfof a rusted carna- flow to the threads of mycelium* 

 tion, showing the intercellular mycelium _..i- f u AV enrmlv material fnr it* 



and haustoria. object magnified 3 o times where they supply material ror its 



continued growth and later for the 



development of the reproductive bodies. Some of these fungus 



parasites often deform their host, stimulating the tissues to the 



* Mycelium is the special name of the fungus threads. 



Fig. 97- 



Rust of carnation stems and leaves caused by a 

 parasitic fungus (Uromyces caryophyllinus). 



