CAUSES OF THE ATTACKS OF RUST, &c. 109 



cereals appear to be fulfilled. It is commonly remarked 

 that rust is most prevalent on new land; this is perhaps 

 explained by the large amount of vegetable matter thrown 

 into a state of decomposition by excess of air and the con- 

 sequent production of ammonia. There is no doubt that 

 much of the ammonia thus generated would combine with 

 vegetable acids, and be fixed by clay, &c. ; but some por- 

 tion could not fail to combine with carbonic acid, and es- 

 cape into the air in the form of the volatile carbonate, as is 

 observed to a great degree on manure heaps even where 

 gypsum or other solid fixers of ammonia are employed to 

 avoid it. We must regard new land as a storehouse 

 of ammonia and other plant food which become liable 

 to volatilize when liberated by too free an exposure to 

 air without proper precautions. If the supposition be 

 correct that "rust" is mainly occasioned by the con- 

 currence of mists or fogs in July or August, rich in 

 ammonia, stimulating the growth of the sporules in the 

 stagnated juices of the plants, and that the active agent in 

 inducing the sudden appearance of that destructive para- 

 site is really ammoniacal vapours, we have a remedy at 

 hand which promises, when properly and carefully applied, 

 if not entirely to check, at least so far to arrest the growth 

 of the parasite as to claim a general trial, especially as its 

 effects would probably prove equally availing in arresting 

 mildew. What we require is an available absorbent of 

 ammonia and its volatile compounds; not an absorbent 

 which will destroy this valuable plant food, but one which 

 possesses the property of inducing it to assume another 

 form, perhaps equally available as a fertilizer, although of 

 much slower action. Eecent observations show that pow- 

 dered charcoal answers these requirements. Charcoal not 

 only absorbs ammonia to an immense extent, but it also 

 oxidises it to nitric acid, and thus renders it temporarily 

 inert, but not unavailable to future fertilization. Powdered 

 charcoal is distributed with the utmost ease over large 

 areas. Being an extremely light substance, and easily re- 

 duced to a fine state of division, the least breath of air is 



