PARASITES AND SAPROPHYTES 



93 



136. Bacteria, much 

 magnified. 



between the food and the saprophyte. The roots of the 

 coral-root (Fig. 132) are covered with this fungus, and 

 the roots have practically lost the power of absorbing 

 nutrients direct. These fungus-covered roots are known as 

 mycorhizas (meaning "fungus root"). Mycorhizas 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 fungus- 

 threads perform some of the offices of root- 

 hairs to the host. On the other hand, the 

 fungus obtains some nourishment from the host. The 

 association seems to be mutual. 



197. Some parasites are green-leaved. Such is the mistle- 

 toe. They anchor themselves on the host and absorb its 

 juices, but they also appropriate and use 



the carbon dioxid of the air. In some 

 groups of bacteria the process of photo- 

 synthesis, or something equivalent .to it, 

 takes place. 



198. -Parasitism and saprophytism are 

 usually regarded as degeneration, that is, 

 as a loss of independence. The ancestors 

 of these plants might have been inde- 

 pendent. Thus, the whole class of fungi 

 is looked upon as a degenerate evolution. 

 The more a plant depends on other 

 plants, the more it tends still further to 

 lose its independence. 



199. Epiphytes. To be distinguished 

 from the dependent plants are those that 

 grow on other plants without taking food 

 from them. These are green-leaved plants 

 whose roots burrow in the bark of the 



host plant and perhaps derive some food i ea f. 



137. A parasitic fungus, 

 magnified. The my- 

 celium, or vegetative 

 part, is shown by the 

 dotted - shaded parts 

 ramifying in the leaf 

 tissue. The rounded 

 haustoria projecting 

 into the cells are also 

 shown. The long 

 fruiting parts of the 

 fungus hang from the 

 under surface of the 



