256 071 Forms of the Hop 



Plants 12, 13, 14. Ref. Nos. V91, V92, V93. Sex unknown. 



P/a«^. 12, 13, 14 |i9j, (.(j^ 



1918. All 3 plants now in H: Ref. No. V91 (Si), 



V92(S'), 

 V93(Si). 



These three seedlings as 2-year-old plants proved persistently 

 immune in the greenhouse during 1916, and again during 1917^. In the 

 autumn of 1917 they were planted out in the hop-garden, the plants 

 grew during 1918 to the height of 5 ft. and all showed slight sus- 

 ceptibility — a very few patches of mildew being present on a few leaves 

 both of V 91 and V 92, and one patch only on the under-surface 

 of one leaf of V 93. 



Plant 15. Ref. No. Z 14 o" PInnI 17. Ref. No. OB 34 $ 



1917 H(I), 1917 H(I), 



1918 H(Si);3 "cuts" 1917/18 G (I). 1918 H (Si); 3 "cuts"' 1917/18 G (I). 

 Plant 16. Ref. No. Z22 ? Plant 18. Ref. No. HH44 $ 



1917 H(I), 1917 H(Si), 



1918 H(S-);2 "cuts" 1917/18 G (I). 1918 H (S^); 3 "cuts" 1917/18 G (I). 



The above four seedlings all agree in their "cuts" being immune 

 when grown in the greenhouse, although all the parents show some 

 degree of susceptibility when grown in the hop-garden. Z 14 showed the 

 merest trace of mildew on its leaves; Z 22 a fair amount of mildew on 

 its "hops" and very occasionally a trace of mildew on its leaves; OB 34 

 was immune in 1918 except for one quite young "hop" (strobile) which 

 alone was smothered in mildew in the conidial stage, and arrested in 

 development, among some hundreds of healthy "hops"^; HH44 

 showed in both years only a trace of mildew in its "hops." 



The evidence given by seedlings in Group 3 shows clearly that one 

 and the same plant^ niay be persistently immune when grown in the 

 greenhouse and susceptible even to the highest degree when grown in 

 the hop-garden. 



Growp 4. 4 seedlings. 



Instances of "semi-immunity" have been noticed in the case of 

 four seedlings. With regard to the seedlings Z 15 (J) and OC 6 (J), one 



1 These are three of tho seven seedlings noted in (]), p. 450, and (2), p. 88. 



2 This case may possibly be compared with the strictly local susceptibility shown l)y 

 one leaf of the "immune" plant of OR 38 in the greenhouse in 1917 (see (2), p. 86). 



3 Adopting Dr J. Schmidt's terminology (see Comples Rendus Trav. Labor. Carhherg, 

 XI, 153 (1915)) each "cut" taken from the parent plant is a "clone-plant," — the "hop- 

 clone" being all those plants derived from the same seedling by vegetative propagation. 



