28 DISEASES OF TROPICAL PLANTS CH 



wet. Some spores will persist in the soil for many 

 years without germination, unless brought in contact 

 with suitable hosts when they germinate very readily. 

 Some spores must undergo certain periods of rest before 

 they will germinate, even though the conditions for 

 germination may be favourable. When the conditions 

 are favourable the spores germinate, producing a thread- 

 like mycelium which penetrates the host, if it be a 

 parasite, or the food body, if it be a saprophyte, in a 

 manner peculiar to itself. In some cases the parasite 

 enters the host through the stoma, in other cases 

 directly through the cell wall, and in other cases 

 through wounds. 



Habits. Fungi feed upon nearly all kinds of 

 living and dead organic bodies, both animal and plant. 

 They may live upon insects, and are no doubt very 

 important in holding this class of pests in check. 

 Sometimes there is an outbreak of disease among 

 insects which becomes a veritable epidemic, and destroys 

 them in enormous numbers. These insect diseases 

 sometimes attack the larvae only, and at other times 

 the mature insects (see page 260). 



Some species attack fish (see page 34), and 

 thousands of fish die each year from this cause. If 

 the aquarium is not properly cared for, or the pool or 

 stream of water becomes low and foul, the fish are 

 likely to contract these diseases. Injured fish and 

 young fish in the hatcheries are especially subject to 

 them. 



Birds and barnyard fowls are also subject to diseases 

 which are caused by fungi, which cause inflammation 

 of the respiratory organs and scab diseases of the combs 

 and crops. Cattle, horses, and sometimes men suffer 

 from a fungus disease known as lumpy jaw, which is 

 contracted from the fungus on the food. The fungus 

 no doubt gains entrance to the tissues through very 

 slight wounds which, in the case of the lower animals, 

 are easily made by the rough edges of the blades of 

 grass. Kabbits, cats, dogs, many other lower animals, 



