126 PRIZE ESSAY : 



gypsum, finely powdered, may be sown broadcast ; under all cir- 

 cumstances they will act in a favorable manner either as a.partial 

 preventive of mildew and rust, or as a manure, by fixing the 

 ammonia of the atmosphere. 



225. The connection of rust with ammonia is exemplified in 

 many different ways. We often find, for instance, that richly 

 manured fields are liable to rust ; and where isolated patches of 

 manure or droppings of cattle occur in a field of wheat, the 

 grain growing on those patches will be rusted generally, but not 

 always. Charcoal beds have long been considered "rust proof" 

 in the United States. Liquid manure, when applied to crops, 

 has proved very beneficial in enabling them to escape rust, while 

 neighboring crops, manured in the ordinary way with solid farm 

 yard manure, were much affected. In one case the ammonia 

 would be all absorbed, in the other case part would return to the 

 atmosphere. Damp situations, fogs, and the season of the year 

 when the decomposition of vegetable matter is most active, and 

 therefore the atmosphere often charged with ammonia, are all 

 conducive to the propagation and development of this fungus. 



226. Rust does not appear to be found on those parts of the 

 wheat plant which are not exposed to air and light, such as the 

 roots, and those portions of the stem enclosed in the sheath of 

 the leaves. This arises from the simple circumstance that there 

 exist no stomata in those parts which are not exposed to light, 

 hence a species of negative evidence that a large proportion of 

 the sporules of rust enter the stomata directly from the air, and 

 vegetate there. Fries states that the sporules of certain fungi 

 are so inconceivably minute that they rise like thin smoke into 

 the air by evaporation, and are dispersed in innumerable ways. (!) 

 He calculated that in one individual fungus the number of seeds 

 exceeded ten millions ; and Mr. John J. Thomas, of Wayne 



(1) Quoted by the author of " Blights of the Wheat." 



