COLLECTION OF STATISTICS. gI 
are cloudy weather (especially if prolonged), sunny weather, frequent or excessive 
fogs or dews, amount of rainfall, and frequency of rainfall, snowfall, hail, excessively 
hot weather, cold spells and frosts, droughts, daily maximum and minimum tem- 
perature, prevalence of special diseases correlated with special peculiar conditions, 
absence of other diseases, etc. 
NATURAL METHODS OF INFECTION. 
Under this heading the student should be on the watch for transmission of the 
disease through fungous or insect injuries, by mollusks, by birds or quadrupeds, 
and by the hand of man. Man contributes to the spread of diseases in various ways, 
Fig.£75.* 
é.g., by neglect to remove diseased plants, by use of infected knives and other 
tools, by the introduction of infected seeds, or manures, or soils, or water, and by 
subjecting his plants to a variety of depressing and unwholesome conditions. 
A great variety of parasites find their home in the earth, the top crust of which 
swarms with bacteria and fungi. Such parasites are frequently introduced from one 
locality to another in infected soils adhering to wagons and other farm tools, to the 
feet of men and animals, to the roots of transported plants, etc. The soil is a living 
thing and it should not be transported even from one field to another on the same 
*Fic. 75.—Bacterium Stewarti filling the substomatic chamber and pushing out into the deeper 
tissues of a maize leaf. The result of an inoculation made by placing a small quantity of a pure 
culture on the tip of a sweet-corn leaf in the seedling stage. For orientation see fig. 74. ‘The glo- 
bose bodies are nuclei, which are not enlarged (?). 
