E. S. Salmon 157 



It is interesting to find that the majority of the seedlings fall into 

 the class in which susceptibiUty in the open varies from to S^. Of 

 these seedhngs six (V 92, V 93, Z 14, Z 31, OR 39, OY 18) are males, 

 and five (V 91, Z 25, OA 49, OB 34, OD 19) are females. The injury 

 caused by the mildew to plants which show a susceptibility of only S^ 

 grade would be neghgible from the practical or commercial standpoint, 

 so that these twelve seedlings could be classified as "commercially 

 resistant^." 



The six seedlings (OE 14, DD 31, HH 20, HH 44, II 13, 316) which 

 so far have shown only S^ in the open would similarly come into the 

 "commercially resistant" class, if they can be considered sufficiently 

 tested. 



The two (female) seedlings (Z 20, Z 22) which have varied in sus- 

 ceptibiUty in different seasons from to S^, and the one (female) seedling 

 (OA 34) which has varied from S^ to S^ have so far suffered so little 

 injury from attacks of the mildew that they also can be included in the 

 class of "commercially resistant," notwithstanding the fact that the 

 grade of susceptibility may reach to S^. 



The (female) seedhng OR 38 has varied in susceptibiUty from S^ to 

 S^, and in the season of 1918 (and to a less extent in 1917 and 1920) the 

 crop of hops was appreciably damaged. It is perhaps significant that 

 this is the seedUng which showed one season a local and temporary 

 susceptibiUty in the greenhouse (see above, p. 154). 



While, therefore, as OR 38 clearly shows, the possession of immunity 

 under greenhouse conditions is not infalUbly an indication of immunity, 

 or even of "commercial resistance," in the open, it does appear that at 

 any rate a majority of the seedUngs which show immunity in the green- 

 house possess, when grown in a hop-garden under commercial conditions, 

 a sufficiently high degree of resistance to be classified at "commercially 

 resistant." 



In all, 301 cuttings, taken from most of the 27 seedUngs enumerated 

 above, have been rigorously tested in the greenhouse from 1917 to 1920, 

 and aU have been found to be immune. In no case has any seedUng of 

 the wild hop which has proved immune in the greenhouse in any one 

 season shown susceptibiUty when cuttings from it have been tested in 

 the greenhouse in other seasons. Cuttings have been taken from "im- 

 mune" seedUngs {e.g. Z 2, Z 14, Z 25, Z 42, OB 34) after they have been 

 growing for five years in a fairly heavily manured hop-garden, and from 



^ To remove any possible misconception, it may be stated here that none of these 

 seedlings of the wild hop have any direct commercial value. 



