E. 8. Salmon 89 



tinuously exposed to infection throughout the seiison ; all the pliintH 

 remained jx^rsistently immune, just jus in lOKi. 



Trial was now made ot* a yellow-leavi'd fi«malc variety purchaned 

 from Messrs Hunyaixl, Maidstcme, in 1912. The plants used were "cuts" 

 taken from established plants in the hop-garden and put into |)ots in 

 the winter of 1916— 17. 



Exper. H. The two plants used were both potted "cuts," one (Ref. 

 No. ^89) was a seedling of the wild hop from Italy, and the other 

 (Ref. No. 341) was the yellow-leaved variety obtained from Messi-s 

 Bunyard. On both plants 1 leaf (at the 2nd node from the apex) on 

 shoots of equal length was inoculated at two places with conidia from 

 the same source. Owing to the abnormal weather conditions (see above, 

 p. 84) it was not until the 24th day that any infection was visible on 

 ZS^\ and then only a few weak conidiophores occurred at one of the 

 places of inoculation ; by the 33rd day weak, clustered conidiophores 

 were visible at the two places on the leaf (which was now brown at the 

 edges), and small, vigorous powdery patches occurred on three other 

 leaves and at one place on the stem. No trace of infection resulted on 

 341, although this plant stood by the side of Z39 throughout the 

 growing season. It was clear that the abnormal weather conditions 

 had no effect upon the immunity of this yellow-leaved plant. 



Exper. 9. Two "cuts" in pots of -^39 and 341, with shoots of six 

 nodes and of equal length, were used in this experiment. The tw^o 

 shoots were first " atomised " with water and then inoculated by shaking 

 over them a virulently infected hop-plant, from which the conidia fell 

 in clouds, — with the result that most of the leaves on both shoots 

 became visibly whitened with the mass of conidia. By the 11th day 

 6 leaves of Z 39 w^ere heavily infected, many of the patches of mildew 

 already bearing clustered conidiophores. By the 15th day 7 leaves 

 and parts of the stem were smothered over with powdery patches. No 

 trace of infection occurred on 341, which stood by the side of ^39 

 throughout the season. 



Exper. 10. Shoots of ZS9 and of 341 of equal length and vigour 

 were selected, and 2 leaves on each shoot — one partly unfolded leaf at 

 the 2nd node fnjm the apex and one just expanded leaf at the 3rd node 

 — were inoculated at three places on each leaf. By the 13th day the 

 2 leaves of ZS9 were infected at all six places; by the 20th day the 

 2 inoculated leaves bore densely powdery patches, and 3 other leaves 

 were also mildewed. By the 30th day 14 leaves of Z39 were mildewed. 



