THE POTATO 207 



burrows is scraped out and examined with the 

 microscope, it will be found to contain numerous 

 eggs, larvae, young and adult worms like those 

 figured in the illustration. The potato cells have 

 broken walls and the starch grains are fewer in 

 number than in healthy tissue and those present 

 are of smaller size. 



'*The disease is spread by planting infested seed 

 potatoes. We do not know to what extent the 

 worms may hve and multiply in the soil itself or 

 how long a soil may remain infected. This impor- 

 tant point can be settled only by careful obser- 

 vation and experiment. 



"How to free infected soil from the parasite is a 

 question which the knowledge at present at our 

 command will not permit us to answer satisfac- 

 torily. Sterilization or disinfection on so large a 

 scale is not practicable. Possibly deep plowing, 

 letting the ground lie fallow for a year, or, where 

 feasible, covering the fields with water during the 

 winter months, may prove to be ejfifective. The 

 best advice for the present, it seems to us, is to 

 plant infected fields with some other kind of crop, 

 preferably grain or alfalfa rather than a root crop, 

 such as sugar-beets, which might be attacked by 

 the same pest. " 



