E. S. Salmon 297 



Among the 21 '' susceptible"' seedlings of "1/17 " there were (1) one 

 ))lant "semi-immune," i.e. the plant showed no infection except that on 

 ^me leaf there were five tiny pale spots on which a weak growth of 

 conidiophores occurred; (2) one plant very slightly normally sus- 

 ceptible; (3) two plants very susceptible; while (4) the remaining 

 plants were normally susceptible, inclining towards the slightly sus- 

 ceptible side. 



Among the 12 "susceptible" seedlings of "3/17" two plants were 

 shghtly susceptible, with the production of normal, small patches of 

 mildew ; one plant was very susceptible ; and the remaining plants were 

 normally susceptible. 



All the "immune" seedlings in both cases were entirely immune. 



Among the above 105 seedlings there was a great difference of colour of 

 the leaf; some seedlings were as "golden" leaved as the female parent; 

 others had a normal green leaf; and intermediate shades occurred. No 

 attempt was made to classify these seedlings on a leaf-colour basis, as 

 owing to culture in the greenhouse there was a tendency for the 

 green-leaved plants to acquire a pale- or yellowish-green tint due to 

 the special conditions. It was clear, however, that there were some 

 plants with green leaves and resistant to mildew under greenhouse 

 conditions. 



These 105 seedlings have been planted out in the hop-garden at 

 Wye College, with the object of investigating them in the open in future 

 seasons as regards (1) sex, (2) colour of leaves, (3) vigour of growth, 

 (4) susceptibility to mildew, and (5) commercial value. 



(2) Seedlings raised at Wye from seed of the -'wild hop" 

 {H. Lwpulus) obtained from Vittorio, Italy. 



In 1919 cuttings of certain seedlings of the above origin were grown 

 in pots in the greenhouse and tested for resistance to mildew both by 

 being surrounded throughout the season by mildew-infested hop-plants 

 and also by direct inoculations with conidia. While, as in past seasons, 

 numerous clone-plants of other seedlings of the same parentage and age 

 and treated in the same way quickly became infested with mildew (which 

 persisted on them throughout the season), the following seedlings proved 

 to be immune, the entire plant remaining absolutely free from any trace 

 of infection. 



Four of the following seedlings (viz. Z 17, OY 18, II 24, II 30) had not 

 been tested in this way before; the remaining 15 seedlings had shown 

 the same resistance in previous seasons (see (3)). 



