Chapter III. 



Fungi* Fungus Life Methods, 

 Jff 



Parasitism and saprophytism. \Ye have already seen how 

 fungi have adopted two methods of nutrition, the parasitic and 

 the saprophytic. It may now be pointed out that there is asso- 

 ciated with these methods of nutrition a further difference, viz. : 

 that of reaction to certain impulses. When a certain parasite 

 comes into close contact with a suitable host plant, it is at- 

 tracted or reacted upon by that plant. In other words, it re- 

 ceives an impulse from that plant which results in certain pecul- 

 iarities of growth, e. g., the sending out of sucker threads or 

 organs, and the final result is the parasitic mode of nutrition. 

 The saprophyte cannot respond to this impulse, no matter how 

 closely its threads may be associated with another plant. It 

 has not learned to respond and so is forced to obtain nutriment 

 in other ways, i. e., in the saprophytic mode. Some plants, 

 however, seem to have partially or imperfectly learned to avail 

 themselves of the parasitic habit, while during the greater part 

 of their lives they are true saprophytes. That is to say, at 

 times in their development they may become parasitic, though 

 they are nominally saprophytic. Such are known as half- 

 saprophytes. Some of the blue molds and especially the wound 

 parasites of trees furnish good examples. Again there are cer- 

 tain fungi which are for the greater part of'their lives parasites, 

 but which are capable of passing, even for a considerable period 

 of time, to a saprophytic habit. Some smuts are able to do 

 this. Such plants are known as half-parasites. True sapro- 

 phytes are those whose whole life is saprophytic, e. g., most 

 mushrooms ; while a true parasite draws nourishment from its 

 host plant throughout the life of the latter. Of true parasites 

 the rusts furnish excellent examples. 



Saprophytes. True saprophytes cannot in any way obtain 

 their nutriment directly from living cells. But since, on account 



