212 TEXT-BOOK OF FUNGI 



but, what is more important to remember, the mycelium 

 also extends into the seed or tubers of the growing plant, 

 consequently the offspring of that particular plant is infected 

 for all time without the fungus ever leaving the plant, and 

 quite independent of spores. The spores produced on the 

 above-ground portion of the diseased plant serve to infect 

 other plants of the same kind, thus securing an even 

 greater extension of the area of disease caused by the 

 particular species of fungus. 



The discovery of this method of propagating a disease 

 by means of hybernating mycelium present in the repro- 

 ductive portion of the host-plant, explains the failure to 

 check certain diseases by means of spraying, and also 

 explains the sudden appearance of a disease in a new 

 district when seed assumed to be free from infection was 

 used. 



The same discovery also suggests the probability that 

 the sudden appearance of an .epidemic, previously assumed 

 to be due to the rapid production and diffusion of spores, 

 may in reality not be dependent on the presence of spores 

 at all, but rather to the presence of hybernating mycelium, 

 which, under favourable weather conditions, developed 

 rapidly and set up an epidemic. 



Infection by means of spores is the most primitive and 

 most general method followed by fungi ; what may be 

 termed the more modern method of infection by means 

 of hybernating mycelium is quite as effectual, and much 

 more economical. When the balance between fungus and 

 host-plant is perfect, infection, by means of hybernating 

 mycelium, which passes from one generation to another 

 without ever leaving the host-plant, is rendered so certain, 

 that the production of spores is completely arrested. 



