260 Variation in Wild Hop 



in 1920 is given in PI. XXV, fig. 2 showing a " lateral " of OD 18 twin- 

 ing round a lateral of OD 19 ; OD 18 is so virulently infected with 

 mildew that no "hops" have been able to develop, all the inflorescences 

 having been turned into little white " knobs," while the hops of OD 19 

 have resisted all attacks and developed normally, quite free from a trace 

 of mildew. 



Complete immunity to mildew was shown by 27 seedlings (13 (/> 

 14 $ ) when grown in the greenhouse. When cuttings were taken from 

 these seedlings after they had been growing for several years (in 

 one case 5 years) in the (manured) hop garden, they showed the same 

 complete immunity in the greenhouse. On the other hand, cuttings taken 

 from other seedlings which showed varying degrees of susceptibility in 

 the Hop-garden were susceptible when grown in the greenhouse. In no 

 case has any seedling which has shown immunity in the greenhouse 

 shown susceptibility there when tested again in other seasons. 



Seedlings immune in the greenhouse show usually some degree of 

 susceptibility when tested in the open, the degree of susceptibility being 

 usually only very slight, but in rare cases reaching to S- or even to S'^. 

 (See Table, p. 259.) 



Certain individual seedlings (7 in number, 4 </ and 3 ?) showed 

 the phenomenon ((6) (7)) of "semi-immunity" when grown in the 

 greenhouse ; these seedlings exhibited in the open also a certain degree 

 of resistance. 



A numerical analysis of the 480 seedlings based on the relative 

 susceptibility to mildew in the open gives us the following figures : 



Totals 480 100 



