268 VEGETABLE GARDENING 



they may be spread in the soil by natural drainage and the 

 land receiving the drainage from infected fields may be- 

 come infected with the disease without ever having had 

 potatoes on them. Scabby seed potatoes when planted on 

 new or old potato land will generally produce a scabby 

 crop, but the amount of the disease will generally be 

 much more on the old land than on the new. 



Perfectly clean seed potatoes planted in soil free from 

 the scab fungus will always and in any season produce a 

 crop of smooth, clean potatoes, no matter what may be 

 the character of the soil ; but apparently clean seed potatoes 

 may have the germs of the scab fungus on their surface. 

 This is often the case where they have been sorted out 

 from a lot that is somewhat infected with scab. In this 

 latter case the tubers should, at least, be thoroughly 

 washed in running water to remove any germs that may 

 be present or, what is better yet, be treated with corrosive 

 sublimate (mercuric bichloride) as recommended below. 



Land infected by the germs of potato scab will pro- 

 duce a more or less scabby crop, no matter how clean and 

 smooth the seed used. 



Scabby potatoes should be dug as soon as mature, 

 since the scab fungus continues to grow on the potatoes 

 as long as they are in the ground. 



Scabby potatoes may be safely used for seed provided 

 they are first treated in such a way as to destroy the germs 

 of the scab that adhere to them. There are many methods 

 of doing this but the most practical now used are as follows: 



Corrosive Sublimate Treatment. Procure from a drug- 

 gist two ounces of powdered corrosive sublimate (mer- 

 curic bichloride); put this into two gallons of hot water 

 in a wooden or an earthenware vessel and allow it to stand 

 until dissolved. Place thirteen gallons of water in a clean 



