E. S. Salmon 155 



as follows. (In 1918 the plants were from 1|^ to 5 ft. high and non- 

 flowering.) 



Ref. no. W 56. 1918: A fair amount of mildew (S^) on the leaves. 

 1919: A trace only of mildew, one hop being destroyed by mildew, and 

 one hop having mildew on the peduncle — otherwise a crop of healthy 

 hops; no mildew on the leaves. 1920: On August 29 there were numerous 

 patches of mildew on three oldish leaves but not elsewhere ; in October 

 there was a fair amount of mildew (S^) on the hops. 



Ref. no. Y 28. 1918: Very mildewed (S^) on the leaves and stems. 

 1919: A trace of mildew on two hops only. 1920: At the end of August 

 there were a few patches of mildew on one middle-aged leaf only; in 

 October there was a fair amount of mildew (S^) on the hops. 



Ref. no. Z4. 1918: Very mouldy (S^) on the leaves. 1919: No 

 observations made. 1920: On August 28 there was one spot of mildew 

 on one leaf; no observations were made in October. 



Cuttings of W 56, Y 28 and Z 4 taken in the winters of 1918-19-20 

 all proved persistently immune in the greenhouse. 



In 1919 eleven cuttings of OR 38 in pots were stood^ in the hop- 

 garden on June 13. On October 23 when all were examined one cutting^ 

 was found to be infected very slightly, there being a tiny "powdery" 

 patch on the undersurface of two leaves. In this season fourteen clone- 

 plants of OR 38 [which were of the same age as the cutting (noted above) 

 which became infected and which had been potted up in similar soil] 

 had been tested in the greenhouse and had all remained persistently 

 immune. With regard to the plants in pots in the open, no mildew was 

 present on them at the end of September. By the date October 23 

 several light frosts had occurred ; it appears, then, safe to infer that the 

 immunity of OR 38 was broken down or partly broken down by certain 

 climatic conditions, possibly low temperature. (The case of Z 25, noted 

 above, also supports this view.) 



Ref. no. OR 39, This seedhng on being raised in the greenhouse 

 from seed in 1914 proved, like OR 38, to be persistently immune. In 

 the hop-garden it showed, in 1916, a trace of mildew, two lateral shoots 

 from the main stem having one leaf each bearing a few mildew-patches. 

 In 1917 one small mildew-patch occurred on the undersurface of one 

 leaf of a lately-developed sideshoot. In 1918, 1919 and 1920 the plant 

 remained free from mildew, although its neighbour OR 38 was infected 



^ The pots were stood on a board, to prevent any contact between the plant, or the 

 soil in the pot, and the soil of the hop garden. 

 - This was a cutting of the clone-plant W 56. 



