POTATO CULTURE. 73 



CHAPTER X. 

 Prevention of Scab. 



Suppose, now, you have selected fine tubers for seed, and 

 have kept them perfectly, so not an eye has started a sprout. 

 There may be here and there spots of what is called scab on 

 them. This is very common now. Or perhaps there were 

 more or less scabby potatoes in your crop the year before, 

 from which your smooth seed was selected. Or, again, you 

 may be so unfortunate as to have nothing but scabby seed, 

 and badly scabby too. You may have some new and costly 

 variety that has scab on, and still you want to use them for 

 seed. In all these cases, what you want to know is, will 

 these potatoes do as well for seed, or does that law of " like 

 begets like " hold good in planting scabby potatoes ? It 

 does, according to our best present knowledge. It is only 

 very recently that we have seemed to get any real light on 

 this point. What we know now, or think we do, is not, 

 perhaps, absolutely a settled fact. Some among our scien- 

 tific authorities still dispute it; but I feel quite certain that 

 Prof. H. L. liolley, of North Dakota Experiment Station, is 

 correct in his conclusions, that the first cause of deep scab is a 

 plant organism, of very minute character, which attacks the 

 surface of the young growing tubers, eroding, irritating, and 

 blackening the adjacent tissues a sort of u bacterioid lun- 

 gus-like affair." This would seem certain, because pure 

 masses of the scab-plant, grown on nutrient gelatin, free 

 from all other germs, when transferred to the surface of 

 healthy growing potato-tubers, will invariably produce the 

 disease at the point of application. 



Knowing this much you will readily see that scabby seed 

 will, under ordinary circumstances, produce a scabby crop. 

 As it is a germ disease, if you selected smooth potatoes out 



