THE SPREAD OF PLANT DISEASES. 127 



have since obtained coniivniatoiy resiilts in otlier places, and am 

 very certain that this disease was in tliat instance spread by way 

 of the manure pile. Probably it is often disseminated in this 

 manner. I shall have more to say of this interesting disease 

 under another head. 



Smut Diseases. — Some of the smut diseases are also Avell 

 known to be transmissible through dung, especially in fresh 

 manure, and for this reason the latter should never be used on 

 fields of cereals. 



Other Diseases. — \yhile not conclusive, the evidence is strong 

 that many diseases come out of the dung pile. I recall a bad 

 outbreak of the so-called timber rot of cucumbers in a hothouse 

 near "Washington where it seemed almost certain that the fungus 

 was introduced with the manure. And within the last six 

 months three cases have come to my knowledge where serious 

 diseases followed unusually heavy applications of manure. One 

 of those was a sclerotium disease of ginseng in Pennsylvania, 

 another the bacterial brown rot of turnips in Maryland, and the 

 third a rot of celery in Florida. 



This subject is at least worthy of much more careful attention 

 than it has hitherto received, and would undoubtedly amply 

 repay all the time put upon it. Manure should at least be kept 

 free from the rubbish of plants that have been attacked by 

 parasitic diseases and ought to be thoroughly composted and rotted 

 before it is used. 



Spread by Way of the Soil. — Certain parasitic diseases 

 of plants are peculiarly soil troubles. Their home is the earth. 

 They live and multiply in the soil indefinitely as saprophytes, and 

 yet are always ready to become parasites when there is an oppor- 

 tunity. Not enough attention has been paid to this class of dis- 

 eases. Among these soil fungi are some of the worst enemies 

 the cultivator has to contend with. They are hidden out of 

 sight, are very difficvilt to combat by fungicidal treatment, and 

 when a field is once well seeded down to one of them it is practi- 

 cally worthless for the growing of such crops as are subject to 

 the disease, the only satisfactory management of the land in 

 most cases being a long rotation with crops not subject to the 

 attacks of the parasite. These soil fungi manage to get aboiit 

 from field to field in various ways. Some of them are known to 

 have been distributed in irrigation water or to have been washed 



