158 Forms of the Hop resistant to Mildew 



one seedling (OR 38) after it has shown a high degree of susceptibility 

 (S^) in the hop-garden; in all cases the cuttings have shown the original 

 persistent immunity. There is no indication so far that cultivation has 

 had any efiect whatever in changing or modifying the original inherent 

 "constitutional" character of the seedling. 



As will be seen from Table IV, tests have been made in various 

 seasons with certain seedlings to prove the continuance of their sus- 

 ceptibihty under greenhouse conditions. Not only seedUngs which are 

 mildewed to the degree S^ in the open, but also seedhngs, like OA 25, 

 which in certain seasons show only a trace of mildew in the hop-garden, 

 proved fully susceptible in the greenhouse. 



If we contrast the excessive susceptibiUty under greenhouse con- 

 ditions of the cuttings of the seedlings Z 24, Z 26, Z 41 and OD 18 with 

 the absolute immunity of the cuttings of Z 25, Z 42, OD 19 — remember- 

 ing that all the cuttings were taken at the same time from the parent- 

 plants which had been growing for five years in the hop-garden within 

 a few feet of each other — we have the most convincing evidence of the 

 permanence of different "constitutional" characters in seedlings of the 

 wild hop. 



(6) "Semi-immunity'^ under greenhouse conditions. 



On reference to Table III, it will be seen that 7 seedhngs (Z 15, 

 Z23, Z38, 0C6, BB 5, OA 33, OD 17) have shown "semi-immunity" 

 in the greenhouse. The behaviour of these seedhngs in the hop-garden 

 has been as follows : 



Ref. no. Z 15. 1917, 1918, 1919: A medium attack of mildew (S^) 

 on the hops. In 1917 and 1918 its neighbour Z 16 was mildewed to the 

 extent of S^. In 1920 Z 15 showed on several of its youngest leaves the 

 arrested or circumscribed development of the mildew-patches character- 

 istic of "semi-immunity"; otherwise the plant was free from mildew. 



Ref. no. Z23. 1917: Mildewed to the extent of S^ on the hops. 

 1918: No mildew present. 1919: A trace of mildew. 1920: No suitable 

 material present. The neighbouring seedhng Z 24 was so susceptible that 

 each season it became mildewed to the highest degree, and in 1918 and 

 1920 the crop was destroyed by mildew. 



Ref. no. Z 38. 1917, 1918: Mildewed to the extent of S^ on the hops. 

 1919: No mildew present, although some of the lateral shoots of Z 38 

 twined round the stems of Z 39, which bore very mildewed hops. Z 39 

 has each season been attacked S^, and in 1918 had its crop entirely 

 destroyed by mildew. 



