308 071 Foimis of the Hop resistant to Mildew 



surface of the leaf; these conidiophores were not sufficiently aggregated 

 anywhere to form a white "powdery" patch — indeed, in most places, 

 they could only be seen when the leaf-surface was examined carefully 

 in a good light. In the ninth seedling infection resulted in the production 

 of pale blotches (scattered over the leaf) on which a weak growth of 

 mycelium and conidiophores took place. 



All the above "4/17" seedlings have been planted out in the hop- 

 garden, so that their behaviour in the open with regard to susceptibility 

 to mildew can be studied. 



3. A FORM OF E. AMERICAN us (cJ). 



In 1914 Dr W. W. Stockberger, of the U.S. Department of Agriculture, 

 sent me cuttings of an American hop, labelled 7 A, 7 C, 7 H. One plant, 

 labelled 7 A, proved during 1918 in the greenhouse to be persistently 

 immune to mildew. During 1919 the same plant of 7 A, together with six 

 other cuttings taken during the winter of 1918-19 from clone-plants of 

 7 A growing in the hop-garden at Wye College, were exposed constantly 

 in the greenhouse to infection by conidia throughout the season. All 

 the seven plants remained entirely free from mildew. Cuttings of 7 C 

 (two plants) and 7 H (one plant) taken at the same time from plants in 

 the hop-garden, and treated' in the same way in the greenhouse, proved 

 susceptible — 7 H being susceptible to a normal degree, and 7 C being 

 very susceptible. 



The above plants were sent to me by Dr Stockberger labelled 

 "Golden Cluster" — which is a commercial variety of hop cultivated 

 in the United States. While, however, the single plants of 7 C and 

 7 H which have flowered have proved to be pistillate and doubtless 

 belong to the variety "Golden Cluster," all the (three) plants of 7 A 

 which have flowered are staminate. This male plant certainly belongs 

 to H. americanus and not to H. Lupulus, as it agrees in every way 

 with the former species, which, as has been pointed out (4), is easily 

 distinguished by the male inflorescence. Dr Stockberger has sent me 

 the following information: "I am surprised to learn that the plants 

 I sent you of my Number 7 A (Golden Cluster) all proved to be 

 staminate. The original plant Number 7, from which cuttings 7 A, 

 7 B, 7 C and 7 H were taken, was obtained by me from a hop-field at 

 Cosumne, Cal., Feb. 25, 1907. The original plant Number 7 was set in 

 my hop-garden here at Washington, D.C., where it regularly bore good 

 hops up until the time the clones were obtained and sent to you. At 

 the same time the cuttings were sent to you, duplicates were re-planted 



