CONTENTS 



INTRODUCTION 



PAGE 



Prevalence of diseases at the present day, as compared with by- 

 gone times Diseases due to physiological causes. Effect 

 of ' rapid transit ' on distribution of disease The necessity 

 of quarantine as a means of preventing the introduction of 

 diseases into new countries, ...... 1-2 



PRIMARY AND SECONDARY CAUSES OF DISEASE 



Primary cause often masked by more obvious effects of secondary 

 cause Wound parasites always secondary causes Ex- 

 amples of primary causes The presence of one parasite 

 often prepares the way for a second parasite, ... 3-5 



EPIDEMICS 



Epidemics sporadic in their occurrence. Epidemics may be due 

 to infection by means of spores, or to the presence of 

 perennial mycelium Influence of atmospheric conditions 

 on the appearance of an epidemic Epidemics favoured by 

 man's influence, ........ 5" 10 



HOW PLANTS ARE INFECTED BY FUNGUS SPORES 



Infection by spores often confined to certain host-plants Chemo- 

 tropism Infection often occurs during the night Suscepti- 

 bility to disease ' Soft ' foliage, 10-14 



HOW FUNGUS DISEASES ARE DISSEMINATED 



By means of spores By a vegetative method, as hibernating 

 mycelium, sclerotia, etc. Wind an important factor in 

 dissemination of spores, also animals, slugs, insects, etc. 

 Man is responsible for a considerable amount of disease, 

 due to ignorance or carelessness in not properly dealing 

 with diseased material Symbiosis between fungus and 

 host-plant, 14-23 



