90 Resistance to Mildew in Hops 



No trace of infection occurred on 341, which stood by the side of Z39 

 throughout the season. 



Six plants of this " golden hop " (341) from Messrs Bunyard stood 

 exposed to infection in the greenhouse throughout the growing season ; 

 all remained persistently immune". 



The " golden " leaved plants (mentioned above) obtained from Messrs 

 Bide and Bunyard are both female, and agree in the characters of the 

 shape of the leaf and its coloration. A comparison of mature plants 

 to establish the identity of the two has not yet been possible. 



In 1917, as in all previous seasons, the 9 plants ("hills") of the 

 " Golden Hop " planted in the hop-garden showed no trace of mildew 

 on leaves or hops throughout the growing season. 



A male variety possessing "golden" leaves also exists. In 1910 

 some plants were sent to me by Messrs Bunyard under the impression 

 that they were the female plant. These were used in the following 

 experiments. 



Exjper. 11. A young leaf (half expanded) on a shoot. 2\ feet long of 

 a " cut " in a pot was inoculated with conidia from the same source, the 

 three following plants being used : (1) a seedling (Ref. No. 0032) of the 

 cultivated variety " Bramling " ; (2) the Russian variety " Shpaltski " ; 

 (3) the (/ variety with yellow leaves. By the 7th day the leaf on all 

 the plants was equally and virulently infected; the leaf (now fully 

 expanded) being covered over almost continuously with densely clustered 

 conidiophores. 



Exper. 12. Young leaves (partly expanded) on shoots of equal 

 length of the Russian variety " Zemshevi " and the (/" variety with yellow 

 leaves were inoculated. By the 7th day the yellow-leaved plant showed 

 infection at the three places of inoculation ; the '' Zemshevi " variety 

 was also similarly infected. 



Three other " cuts " in pots of the ^ variety with yellow leaves were 

 placed in the greenhouse and exposed to inoculation by placing viru- 

 lently infected plants around them. They all became infected. It is 

 clear that this ^f plant with yellow leaves is susceptible to a normal 

 degree to /S. Hiiirndi. 



1 An attempt was made to induce susceptibility by injury to the leaf. A young leaf of 

 341, attached to the stem, was pricked with a pin, 30 holes being made in the half of the 

 lamina on one side of the mid-rib. The injury inflicted did not kill the leaf cells except 

 those immediately surrounding tlie hole. The whole leaf was inoculated, but no infection 

 resulted. 



