88 Resistance to Mildew in Hops 



to mildew. Whether the resistance to mildew as shown in 1914 by the 

 original seedling plants of OJ?38 and Oi2 39, and in 1917 by the "cuts" 

 taken from them, will be found to disappear after the plants have been 

 grown for some time in manured ground remains to be seen. It is 

 intended to carry out inoculation experiments with "cuts" taken in 

 successive years. 



We will consider now the behaviour in 1917 of the seven seedlings 

 of the wild hop from Italy which showed immunity in 1916. 



Exper. 6. One of the above seedlings (plant a) and another seedling 

 of unknown susceptibility (plant b) of the same parentage and age were 

 inoculated. Each plant was inoculated at three places on 2 leaves (at 

 the 2nd and 3rd node . from the apex), the shoot of each plant being 

 of the same length and apparent vigour. By the 18th day plant h 

 was infected on one leaf at the three places, where there were large 

 patches of densely clustered conidiophores. By the 27th day the other 

 leaf of plant h showed patches of mildew at two of the three places of 

 inoculation. The plant a showed no trace of infection. 



For the remainder of the growing season this immune seedling a 

 together with the six other immune seedlings of 1916 stood in the 

 greenhouse among some hundreds of virulently infected hop-plants, 

 under conditions which ensured a continual inoculation of their leaves 

 and stems with conidia. None of these plants showed a trace of mildew. 

 For two consecutive years, then, these seven seedlings of the wild hop 

 from Italy have proved persistently immune under conditions in which 

 other seedlings of the same parentage and age have proyed very sus- 

 ceptible. Three of these seven immune seedlings have now been 

 planted out in the hop-garden. 



Group (b). Complete immunity to mildew was shown in 1916 by a 

 form of H. Lupulus with yellow leaves obtained under the name of 

 "golden hop" from Messrs Bide and Sons, Nurserymen, Farnham. This 

 plant was further tested in 1917 in the following experiments. 



Exper. 7. Two leaves (at the 4th node from the apex) on a plant 

 of the "golden hop" obtained in 1916 from Messrs Bide, and on a 

 two-year-old seedling hop of unknown susceptibility, were inoculated at 

 three places on each leaf By the 10th day the latter plant bore large 

 densely powdery patches of mildew at the six places of inoculation. No 

 trace of infection was visible at this date, or subsequently, on the 

 " golden hop." This plant, together with three other potted " cuts " of 

 the " golden hop " from the same source, stood in the greenhouse con- 



