262 Variation hi Wild Hop 



percentage of seedlings occurring in the different grades of suscepti- 

 bility. 



In the highest grade of susceptibility, in which the plant was each 

 season mildewed to the extent of S'^, there are 85 seedlings. Our records 

 show that of these 85 seedlings, no less than 34 had the crop of " hops " 

 entirely destroyed by mildew in one or more seasons ^ 



In the next class, the incidence of mildew varied from S^ to *S^* in 

 different seasons. This class comprises 80 seedlings ; of these, 21 

 seedlings were attacked in some season to the extent that the entire 

 crop was destroyed". 



If we add together the numbers 34 and 21, we get 55 as the number 

 of seedlings which have had their entire crop of hops destroyed in some 

 season or seasons. This number represents 18*90 °/^ of the total number 

 of the ? seedlings. 



We may consider the class of 85 seedlings attacked ;S^" each season — 

 representing 29"21 °/^ of the $ seedlings — as exhibiting excessive 

 susceptibility to mildew, probably exceeding that shown by any com- 

 mercial variety of hop cultivated to-day. 



To the class of very susceptible seedlings may safely be added the 

 80 seedlings of the S'^ — S^ class. This gives us 165 seedlings (or 5670 °/„ 

 of the total number) belonging to a grade of susceptibility in which 

 virulent attacks of mildew are common. 



In the class S^, consisting of seedlings which have shown a medium 

 attack of mildew each season, we have 26 plants, or 8'93 °/„ 



In the next class, where the incidence of mildew varies in different 

 seasons from S^ — S^ — that is, from a trace of mildew to a medium 

 attack — we have 48 seedlings, or 16'49'^/„. In this class an appreciable 

 degree of resistance to the mildew begins to be shown by some of the 

 seedlings, but it is in the succeeding classes that this phenomenon is 

 most clearly seen. 



In the class S^, i.e. those seedlings which have shown only a trace of 

 mildew each season, we have 12 plants. Of these, 5 cannot be considered 

 to have been sufficiently tested, leaving us with 7 seedlings which have 

 proved to be persistently resistant in the open. Of these 7 seedlings, 4 are 

 immune and 1 semi-immune, under greenhouse conditions. 



' The actual records for these 31 seedlings are as follows, where the integer gives the 

 number of seedlings, the numerator of the fraction the number of times the entire crop 

 was destroyed and the denominator the total number of seasons during which observations 

 were taken: 2, |; 5, t; 7, J ; 2, §; 7, J; 11, ^. 



2 In all cases S^ f was reached only once by these seedlings, the actual records being 

 as follows : 1, i; 9, J ; 6, A; 5, J. 



