93 



are iibunt equally effective, and one's ehok-e will depend upon the ease with 

 which they can be pi-ocured. Formalin has the advantaf^e of not beins a 

 violent poison like the corrosive sublimate. For that reason. I prefer the use 

 of formalin. — I'lof. John Craitj, Cornell Uiuversiti/. 



Dry-rot of Potatoes (Fusariiim nxtispornm). 



The disease to which the name " dry-rot " h.-is been .^iven is caused by 

 several different fungi, but the one which does the main amount of damage is 

 known as Fusariiim oxijsporinii. a fungus very closely allied to the sleepy- 

 disease fungus of tomatoes. The Fusariiim is fairly prevalent, but is generally 

 not noticed until a considerable time after the tubers have been stored, 

 although the disease is contracted while the crop is growing in the field. The 

 foliage of diseased plants generally waits, but as this does not occur till the 

 tubers are nearly full-grown, very little notice is taken. 



The disease enters the tubers at the stem end and gradually .spreads 

 through them, following the course of the vascular binidles, and thus shows 

 up a discoloured ring when cut across. At first sight one is reminded of 

 potato-bacteriosis, but it can at once be distinguished, owing to the absence of 

 any watery matter oozing out from the discoloured ring. The tubers gradually 

 shrink and the skin becomes wrinkled, while the whole interior becomes trans- 

 formed into a more or less hard, crumbling mass of a gray colour. The fruit- 

 ing part of the fungus appears on the surface of the tubers as specks of white 

 mould, on the delicate filaments of which are produced the characteristic 

 sickle-shaped spores, which are divided into four by transverse septa. Sound 

 potatoes can readil.y contract the disease through coming in contact with 

 diseased ones. Thus the loss that may be sustained through the storing of 

 healthy and diseased tubers together can easily be imagined. 



Trculincnt. 



As this fungus enters the plant below the ground, and may gain access 

 iluring any part of the season, it is difficult to cope with ; nevertheless, the 

 following measures will be found fairly satisfactory: — 



1. Only sound tubers should be used for seed. It is equally imixirtant not 

 to plant potatoes on land where the disease has recently appeared, for this 

 fungus can live in the soil for a considerable time, iirobably for several years. 

 8uch infected land should be used for other crops, such as cereals or grasses. 



2. Collect and burn all badly-diseased tubers and store suspected ones in 

 a cool, dry place, where the temperature remains about 40 Fahr. 



.3. If it is found impracticable to store in a cool place, the tubers should be 

 sold and eaten as soon after harvesting as possible. There is no danger in 

 eating jiartly affected potatoes, as boiling kills the fungus; and even if they 

 were eaten raw the fungus cannot harm human beings, as it cannot grow at 

 ordinary blood temperature. 



4. Nitrogenous manures have been shown to increase the virulence of this 

 disease, hence they should be avoided as far as ijossible. 



Z>. Never throw diseased tubers on the manure-heap ; this is one of the 

 most fruitful sources of the spread of nearly all fungus diseases. 



ti. Spraying with Bordeaux mixture makes the plants much more healthy 

 than the.v would otherwise be, and helps them to resist this disease. 



