E. S. Salmon 253 



house, under the severest tests as regards constant inoculations, for 

 three years. They have now been planted out (during the winter of 

 1918-19) in the Experimental Hop-garden (under Reference Nos. 316, 

 OB 26, OE 14, DD31) with the object of seeing what effect, if any, the 

 different conditions of growth have on their resistance to mildew. 



Gioup 2. 5 seedlings (5-9). 



Plant 5. Ref. No. Z 42 cJ 



1917 H(I), 



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

 Plant 6. Ref. No. Z 2 J 



1917 H(I). 



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

 Plant 7. Ref. No. OD 19 ? 



1917 H(I), 



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

 Plant 8. Ref. No. Z 25 9 



1916 H(I), 



1917 H (I), 



1918 H (I); 4 "cuts" 1917/18 G (I). 

 Plant 9. Ref. No. OA 49 $ 



1917 H(I), 



1918 H(I); 2 "cuts" 1917/18 G (I). 



These five seedlings have all remained immune in the hop-garden, and 

 the "cuts" taken from them in the winter of 1917-18 proved immune 

 in the greenhouse during the growing season of 1918. 



The plant Z 25 first attracted attention in the hop-garden in 1916, 

 since no mildew was present on it while the two seedlings (Z 24 $ and 

 Z 26 $) on either side of it in the same row, and of the same parentage and 

 age, were severely attacked both on the leaves and "hops." The same 

 thing occurred in 1917; Z 24 and Z 26 were excessively mildewed, and 

 it so happened that some lateral branches of Z 24 had grown out, 

 reached the main stem of Z 25 and had climbed up it and produced 

 very mildewed "hops" (strobiles) on branches closely interwound round 

 those of Z 25 which bore perfectly healthy (immune) hops. In the case 

 of the seedling OD 19, a strong lateral shoot grew out and twined round 

 the main stem of OD 18 (a susceptible seedling of the same age and 

 parentage) and produced healthy hops on branches intertwined with 

 those bearing the excessively mildewed hops of OD 18. 



It may be pointed out that with respect to all these seedlings 

 (Z 2, Z 25, Z 42, OA 49, 0D'19), the incidence of the disease in the hop- 

 garden in both 1917 and 1918 was such as to ensure their natural 

 Ann. Biol, v 17 



