] 52 Forms of the Hop resistant to Mildew 



Z 1 (likewise a c? seedling) was infected to the extent of S^ in 1917, 1918 

 and 1919, and S^ in 1920. 



Ref. no. Z 14. In the open slight susceptibihty was shown in 1918 

 and 1920; no mildew occurred on the plant in 1917 and 1919, when its 

 neighbour Z 15 became mildewed to the extent of S^. 



Ref. no. Z 17. In 1917 this seedhng remained free from mildew, 

 while Z 16 was mildewed to the extent of S^. In other seasons there has 

 been no opportunity of testing Z 17 in the open. 



Ref. no. Z 20. This seedling was planted out in 1914; two cuttings 

 taken in 1919-20 proved persistently immune in the greenhouse. In 

 the open the plant was recorded as S^ in 1917; in 1918 as having a trace 

 of mould on leaves and hops; in 1919 it remained free from mildew, 

 notwithstanding the fact that lateral shoots of Z 19, bearing very mil- 

 dewed hops, had twined round its stems. In 1920, Z 20 showed a mere 

 trace of mildew on the leaves, but several hops were infected with 

 mildew at the extreme tip — the susceptibihty being estimated as being 

 between S^ and S^. There can be no doubt that Z 20 has been severely 

 tested in the open, since its neighbour Z 19 has been smothered in mildew 

 each season and in 1920 had its entire crop destroyed. 



Ref. no. Z 22, This seedhng remained free from mildew in 1917 

 (when Z 23 was recorded as S^); in 1918 and 1919 the amount of mildew 

 on Z 22 was S^ on the hops and very occasionally a trace of mildew on 

 the leaves; in 1920 there was a full crop of hops, i.e. none was deformed 

 by attacks of mildew, but very occasionally the mildew occurred on the 

 peduncles — the susceptibility being estimated as being between S^ and S^. 



Ref. no. Z 25. The history of this seedhng is one of the most interest- 

 ing. It was planted out in the hop-garden in 1914. In 1916 and 1918 it 

 remained free from mildew, although Z 24 and Z 26 on either side of it 

 were smothered with mildew, Z 24 in 1918 having all its hops destroyed 

 by mildew. In June 1918 young leaves of the parent-plants Z 24, Z 25, 

 Z 26 in the open were artificially inoculated with conidia ; infection 

 resulted on Z 24 and Z 26, while Z 25 proved immune. In 1917 Z 25 

 remained entirely free from mildew, notwithstanding the fact thatr 

 several strong lateral shoots of Z 24 had become intertwined with those 

 of Z 25 and had produced very mildewed hops which became inter- 

 mingled with the "immune" hops of Z 25. In 1919, at the beginning of 

 August, after a spell of abnormally dull, cold weather, a few small 

 patches of mildew occurred on a few of the young leaves of Z 25. These 

 mildew-patches died away completely as the weather became normal 

 (hot and sunny) and no more mildew occurred on the plant. In October 



