412 BULLETIN No. 127. [August, 



power in varieties.* It has been commonly concluded from general 

 observations by writers on potato culture that such is the case. 

 There are varieties which in comparative tests with others, give 

 small proportions of infected plants for a number of years and then 

 show a notable increase in this proportion. This, however, may be 

 easily explained. In plants propagated by seeds, when the vigor of 

 any particular season's produce has been seriously impaired, the 

 germinating power of the seed is likely to be affected and they are 

 therefore either discarded for planting or fail to produce plants in 

 the field, and the less vigorous strain perishes. With potatoes, an 

 epidemic of any particular disease scarcely ever completely destroys 

 the crop. The tubers weakened in vigor are planted the next sea- 

 son and may possibly produce plants less able to withstand the ef- 

 fects of futher infection. 



We have already seen the possibility of keeping up (not im- 

 proving) varieties by selection, in the discussion concerning the 

 transmission of tuber variations. Girard (45), who had probably 

 a wider experience than any other investigator in the subject, 

 working as he did for eleven years with sometimes over six hun- 

 dred co-operators, sums up the whole matter as dependent on 

 seed selection. However, the strict attention he paid to all matters 

 concerning soil, fertilizers, planting and cultivation shows that he 

 really laid great stress on favorable environment. He says : 



"It is an opinion quite broadly held that varieties of potatoes cultivated con- 

 tinually in the same region, are certain to degenerate. It is a frequent thing to 

 hear large potato buyers or starch manufacturers declare that after having im- 

 ported and placed at the disposal of their growers varieties of potatoes noted for 

 their large crops, they have seen them give excellent results the first year, fall 

 away the second year, and give results even lower than the native potatoes in 

 the third year. This is indeed true but it is by no means inexplicable ; the de- 

 generation which one sees in this circumstance, does not result from a natural 

 weakening of the variety; it simply results from the entire lack of care with 

 which the plants to be perpetuated are chosen. All the good tubers are sold to 

 the market, and it is from the inferior, discarded tubers that has been demanded 

 a continuation of qualities which they cannot give. I have demonstrated prac- 

 tically, and have established the fact that if suitable tubers are selected for 

 planting and the cultivation accomplished with the needed care, the quality and 

 quantity of the crop will be maintained under all satisfactory climatic conditions." 



Since such degeneration as is commonly noticed can be readily 

 explained without resorting to any hypothesis of "variety senility," 

 this division of the subject is still to be discussed. 



*It also may be that there is a natural selection of more virile strains of funei. 



