CAUSES OF THE ATTACKS OF RUST, &c. Ill 



billions. The connection of rust with ammonia is exempli- 

 fied in many different ways. We often find, for instance, 

 that richly manured fields are liable to rust ; and where 

 isolated patches of manure or dropping 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 neighbouring 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 at- 

 mosphere. 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 develop- 

 ment of this fungus. 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 spe- 

 cies 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 

 fungus 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 county, JSTew York, has esti- 

 mated the number of plants of rust on a single wheat stalk 

 to be twenty millions." As affording what may probably 

 be considered a corroboration of the Professor's views 

 above detailed as to the cause of rust, we may note that 

 in our experience dibbled wheat in which the plants have 

 been widely separated, and as a consequence more than 

 usually exposed to the free play of the atmosphere, has 

 always been very much rusted. 



