310 On Forms of the Hop t^esi slant to Mild em 



is susceptible in the greenhouse and in the open. This o form appears 

 to be the one found originally in Germany and described under the name 

 of H. Lupulus aureus. No account of the origin of any $ "Golden hop" 

 has been found in horticultural literature. 



2. Certain seedlings raised from the immune $ "Golden hop" (the 

 ^ parent being unknown) possess green leaves and are immune to mildew 

 when grown in the greenhouse. 



3. Different seedlings of the wild hop {H. Lupulus) have distinctive 

 physiological or "constitutional" characters, which are constant under 

 the same environment. These characters confer immunity or suscepti- 

 bility, or intermediate grades of susceptibility, on the respective seedlings. 

 The immunity is retained by the plant after four years' residence in the 

 manured soil of the hop-garden. 



4. Certain seedlings of the wild hop which show persistent immunity 

 when grown in the greenhouse show some degree of susceptibility when 

 grown in the open. The susceptibility shown is usually very slight. There 

 is some evidence that this breaking down of immunity is due to the effect 

 of certain climatic conditions. 



5. In the great majority of cases, the greenhouse conditions do not 

 have the effect of making seedlings of the wild hop immune to mildew. 

 In the case of some seedlings extreme susceptibility is shown under 

 greenhouse conditions. 



6. The phenomenon of semi-immunity is shown by certain seedlings 

 of various origins. 



7. A form {^) of H. americanus Nutt., obtained from the United 

 States, has proved immune to mildew under greenhouse conditions. 

 Under the same conditions several American cultivated varieties proved 

 susceptible. 



BIBLIOGRAPHY. 



(1) Salmon, E. S. On Forms of the Hop {Humulus LupnJns L.) resistant to Mildew 



{Sphaerotheca Humuli (DC.) Burr.). Journ. Agric. Science, vrn, 455-460 

 (1917). 



(2) Idem, n. Journ. Genetics, vm, No. 2, 83-91 (1919). 



(3) Idem, m. Annals of Applied Biology, v, 252-260 (1919). 



(4) and WoRMALD, H. Uumulus americanus NuttaW. Jourual of Botany, \915, 



p. 132. 



(5) Blodgett, F. M. Hop Mildew. Cornell Univ. Agric. Exper. Sintion Bull., $28, 



p. 291 (1913). 



(6) Further Studies on the Spread and Control of Hop Mildew. N. York 



Agric. Exper. Station Bull., 395, p. 42 (1915). 



