E. S. Salmon 457 



immune plants observed in 1914, a second sowing of the seed having 

 been made in 1915. The resistance to mildew of these seven plants 

 was put to the same tests as in 1914, and all the plants remained immune 

 throughout the growing season. Other seedhngs (to the number of 

 about one hundred and fifty) of the same origin and age and grown in 

 the same glass-house proved highly susceptible to mildew. 



The same complete immunity was also shown, during 1916, under the 

 same circumstances, by a form of Humulus Lupulus with yellow leaves, 

 obtained under the name of "golden hop" from Messrs Bide and Sons, 

 of Farnham. In this case the plants, three in number, were "cuts" 

 taken from an older plant or plants, and potted up the previous autumn. 

 In one experiment, on May 4, 1916, two young leaves of this "golden 

 hop," and one young leaf of a seedhng hop, were removed from the 

 plants, inoculated, and placed on damp blotting-paper in a large petri 

 dish. By May 9 the green leaf of the seedling showed at the place of 

 inoculation several vigorously-growing patches of mildew, with numerous 

 clustered conidiophores ; by May 15 these patches had become densely 

 "powdery." No trace of infection resulted on the leaves of the "golden 

 hop." 



The two immune seedhngs noticed in 1914 were planted out during 

 the winter 1914-15 in the Wye College Experimental Hop-garden, 

 and were sufficiently established by 1916 to grow to the normal length 

 of an adult plant and to produce flowers. One plant proved to be 

 female, the other, male. The season of 1916 was, as mentioned above, 

 notable for the prevalence of "mould" in hops, and in the part of the 

 hop-garden where the two seedhngs were planted the surrounding " hills" 

 of hops showed, during the summer, patches of mildew on the leaves 

 and hops. The two seedlings showed no trace of mildew on any part 

 through the summer and early autumn, although mildew was noticed 

 on all the adjacent plants. In October, however, mildew was observed 

 on both the seedhngs. By October 3 one plant (the female) had pro- 

 duced a late, rather weak shoot ("bine") which had run up round the 

 old stems ("bines") to a considerable height and produced a few hops. 

 On this late shoot alone some of the leaves and one hop bore several 

 small patches of mildew. The other plant (male) similarly remained 

 resistant to mildew throughout the growing season; on October 3 

 two late lateral shoots each showed one leaf with small patches of 

 mildew. 



The further facts as regards the origin of these plants which have 

 shown resistance to mildew are as follows. 



