320 DISEASES OF FIELD & GARDEN CROPS. [OH. 



haulms have been completely destroyed by the parasite. 

 A prize essay on this subject by Dr. Jeffrey Lang will be 

 found in the Journal of the Royal Agricultural Society for 

 1858. Dr. Lang experimented to the full depth of a 

 spade or fork, and double ploughed, the potatoes being 

 early earthed-up, with the result that few or none of the 

 potatoes so grown were diseased. Dr. Lang mentions the 

 case of " a man at Whilborough " who on dry days, in 

 order to save his potatoes, instead of digging them tip, 

 earthed the stalks up very high, and so effectually saved 

 his crops. "It was observed," writes Dr. Lang, "that 

 no potato covered with more than 3 inches of soil was 

 ever diseased," and " I have seen scores of potatoes dug, 

 but I have never seen or heard of one diseased potato 

 being found 4 inches under the surface of the ground. 

 It will be at once seen and too much stress cannot be 

 laid on the fact that the disease is in an exact ratio to 

 the proximity of the tubers to the surface." Dr. Lang 

 also experimented with tubers in the following manner : 

 Three series were planted three deep, and covered with 

 two-and-a-half inches of soil. On two series diseased potato 

 leaves were placed, and then supplied with water through a 

 fine rose ; the third set were covered with a slate. In all 

 three series the under layers of potatoes were found un- 

 diseased ; all were undiseased under the slate ; whilst the 

 upper layers covered with diseased potato leaves were 

 found to be much affected or quite rotten. He ends the 

 essay by saying, " Earthing-up repeatedly with fine earth 

 is the only effectual preventive to the ravages of the 

 disease." 



During the last quarter of a century the subject has 

 been frequently adverted to in the horticultural and agri- 

 cultural papers. In some instances a good result has been 

 recorded, in others a negative one. As commonly prac- 

 tised, the harvest of large tubers is said to be lessened, 

 and in some quarters the extra expense, care, and labour 

 has been greatly objected to. Professor W. G. Farlow, in 



