PARASITES AND SAPROPHYTES 



87 



saprophytes are aided iu securing their food by soil fungi, 

 which spread their delicate threads over the root -like 

 branches of the plant and act as intermediaries be- 

 tween the food and the saprophyte. The roots of the 

 coral -root (Fig. 119) are covered with this fungus, and 

 the roots have practically lost the power of absorbing 

 food direct. These fungous-covered roots are known as 

 mycorrhizas (meaning ''fungus root")- Mycorrhizas are 

 not peculiar to saprophytes. They are found on many 

 wholly independent plants as, for example, the heaths, 

 oaks, apples, and pines. It is probable that the fungous 

 threads perform some of the offices of root -hairs to the 

 host. On the other hand, the fungus obtains some nour- 

 ishment from the host. The association seems to be 

 mutual. 



183. Saprophytes break down or decompose organic 

 substances. Chief of these saprophytes are the microscopic 

 organisms known as 

 bacteria (Fig. 123). 

 These innumerable 

 bodies are immersed in 

 water or iu animal and 

 plant juices, and absorb 

 food over* their entire 

 surface. By breaking 

 down organic combina- 

 tions, they jJroduce decay. 

 Largely through their 

 agency, and that of 

 many true but micro- 

 scopic fungi, all things pass into soil and gas. Thus are 

 the bodies of plants and animals removed and the con- 

 tinuing round of life is maintained. 



184. Some parasites are green- leaved. Such is the 

 mistletoe. They anchor themselves on the host and 



121. Saprophytic fungus. One of tlie shelf fungi 

 (Polyporus) growing on dead trunks and logs. 



