E. 8. Salmon 87 



not inoculiiUKl Ix'camc Riibstvjufntly infecUnl. The haiiic wjih iiltw) the 

 case with one plant of the var. fieo-tfiexinniuM, and with oiw " hybrid " 

 seedling? (Rof. No. ()Cl\2). It is clear that (hiring' the exiKTiinrntH there 

 wfts no ^Mieral breaking down of the " innnunity " of the two 8<»e<llin^ 

 OHllH and ()R:V,K but in the wi.se of O/i 8S. ..nly a .strictly h^cal or 

 UMnporary sustvptibility due to unknown causes. This is confirmed by 

 the general bi»haviour HubsiMjuently <»f these phint^ in the ^reenhruise 

 chirin^ the season. Besides th<' one |)Iant of 0/^3!) and th<* four phints 

 of OH 3H use<i in the above-mentioned Kxjx'riments, an additional 

 potted "cut" of each seedling was present in the greenhouse. These 

 seven phmt.s ma<le during the season a strong, "healthy" grnwth, e^ich 

 producing seveml stems, 4 to 6 feet high, with large leaves of a dark- 

 green colour. Although the conditions were ideal for the growth and 

 dissemination of the mildew — jis was evidenced by the ftict that it was 

 only ni'cessiiry to stand a healthy (susceptible) seedling hop-plant in the 

 greenhouse am<»ng the mildewed plants to find it in a few weeks' time 

 more or less smothered with mildew — these seven plants placed under 

 the siime conditions for several months showed no trace of infection 

 beyond that temporarily induced in Eocpers. 2 and 5. 



The behaviour of the original plants OR 88 and OR 89 may now be 

 noted. These two seedlings proved immune in the greenhouse during 

 the season 1914 ; during the winter 1914 — 15 they were planted out in 

 the Experimental Hop-garden at Wye College. In 1916 they flowered, 

 one {OR 38) proving to be female, and the other, male. During the 

 summer of 1916 both plants kept free from mildew \ although it occun-ed 

 on all adjacent plants ; by October 3rd, however, mildew was observed 

 on both plants. On this date OR SS showed patches of mildew on 

 several of the leaves and on one hop of a late shoot; while OR 39 showed 

 mildew on one leaf each of two late lateral shoots. In 1917 both plants 

 remained free from mildew* until the autumn. In October, however, 

 ORSH showed a fair amount of mildew (with perithecia) on its hops, 

 chiefly on the peduncles but also on the bracts and bracteoles ; OR 39 

 showed one small patch of mildew on the under-surface of one leaf of a 

 lately-developed lateral shoot. 



It is clear, therefore, that both OR 38 and OR 39 when grown in a 

 manured hop-garden produce late in the growing sea.son leaves which 

 are more or less susceptible to mildew, and that OR 38 under these 

 conditions produces "hops" (strobiles) which are decidedly susceptible 



^ No direct inoculations were niade on these plants in the hop-garden. 



