

NUTRITION OF PARASITES AND SAPROPHYTES 137 



214. Nutrition of parasitic fungi. Examples of the para- 

 sitic 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 XXIX and 

 XXX). 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 



Fig. 99. 



Rust of carnation stems and leaves caused by a 

 parasitic fungus (Uromyces caryophyllinus). 



the threads develop spe 

 cialized short branches, simple or branched, which penetrate 

 the cell walls and lie in the protoplasm of the host cell. These 



special branches are the hausto- 

 ria. They absorb food sub- 

 stances which flow to the threads 

 of mycelium* where they supply 

 material for 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 formation of excre- 

 scences or galls, as in corn smut, 

 the cedar apples, azalea apples, black knot of the plum and 

 cherry, leaf curl of peach, plum pockets of the plum, etc. 

 * Mycelium is the special name of the fungus threads. 



Fig. ioo. 



Cells from the stem of a rusted carnation, 

 showing the intercellular mycelium and 

 haustoria. Object magnified 30 times 

 more than the scale. 



