E. S. Salmon 161 



The percentage figures in the two tables given above show a higher 

 grade of susceptibihty among the ? seedhngs than among the S seedlings. 

 It would be unsafe, however, to consider this proved, owing to the cir- 

 cumstance (see above, p. 149) that the observations as to the incidence 

 of the mildew were made at a time pecuharly favourable for attacks on 

 the ? plant. The c? and the ? plants would need to be tested at a time 

 when each provided the same amount of infectible material before any 

 inference could safely be drawn as to their relative susceptibility. Of 

 the 27 seedlings showing immunity in the greenhouse, 14 are $ and 13 

 are o. 



Since excellent material to test the degree of susceptibility was 

 always present each year in the case of the ? plant, it will be safer to 

 use the figures in Table VII rather than in Table VI on which to base an 

 estimate of the percentage of the seedlings in various grades of sus- 

 ceptibihty. 



In the highest grade of susceptibihty in which the plant was each 

 season mildewed to the extent of S^, there are 85 seedlings. Of these, 

 no less than 34 had their crop of hops entirely destroyed 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 seedhngs. Of these, 21 seed- 

 hngs had their crop of hops destroyed by mildew in some season^. If 

 we add together 34 and 21, we get 55 as the number of seedhngs which 

 have had the entire crop of hops destroyed in some season or seasons. 

 This number represents 18-90 per cent, of the total number of the $ 

 seedhngs. 



Referring back to Table VII, we may consider the first class of 85 

 seedhngs showing S^ each season (which represents 29-21 per cent, of 

 the ? seedhngs) as exhibiting excessive susceptibihty to mildew, probably 

 greater than that shown by any commercial variety of hop cultivated 

 to-day. 



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

 80 seedhngs of the S^ to S^ class. This gives us 165 seedhngs (or 56-70 per 

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

 virulent attacks of mildew are common. 



^ The actual records for these 34 seedlings are as follows, where the integer gives the 

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

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

 were made: 2|, 5j, 7^, 2f, 7^, 11^. 



* In all cases S'f ^^^ reached only once bj^ these seedlings, the actual records being 

 asfoUows: H, H> 6^,5^. 



