154^ 



L-ISKASES UUE TO FUXGI, BACTERIA ETC. — GEKERALITIES- 



Species or type of Triticiim 



Percentage infections 



90-99 



50-89 



10-49 



Triticum compactiim 6 



T. dicoccum 24 



T. duri'Vi 45 



T. monococcum 6 



T. polonicum 10 



T. Spelta II 



T. turgidum 7 



T. vulgare 52 



Total ... 161 

 I 



36 



3 

 35 



14 



27 



])e said about the third group with its 27 varieties, especiall}^ in considering 

 the numerous sources of error (conditions of temperatiire, moisture, techni- 

 que, etc.) which often interfere with the results in this kind of work . 



But when, ever>i;hing else being equal, the results always tend to be 

 negative, and when the percentage of infection falls below 50, it must be 

 admitted that the case is different, and that the variety under examination 

 is less susceptible than in those cases where artificial infection is almost 

 alwaj's successful. The varieties Triticum Fitchsii, " Common Emmer ", 

 " Russian Emmer ", " Spring Emmer ", " White Emmer ", and " Rhaphi " 

 of T. dicoccum ; the varieties T. durospermum, T. lihycum and " Malaga " 

 of T. durum ; the variety T . vulgare of T. monococcum and the varieties 

 T. caesium, T. erythrospermum . T. ferrugineum, and T. pyrothrix of T. 

 vulgare, are undoubtedly all immune to a very great extent. 



There are some results of special interest, those wliich have been obtained 

 Vvith the wild wheat of Palestine which is considered b}' many authors to 

 be a distinct species (7 . dicoccoides Kcke.) and by others as a variety' of 

 7". dicoccum. This type of wheat should be very susceptible to the attacks 

 of Erysiphe. 



With the exception of several species of the genus Aegilops which is 

 moreover often considered as a sub-genus of Triticum, all the attempts 

 at infecting grasses of various genera, Avena sativa, Brachypodium dis- 

 tachyum, Hordeum vulgare, and Secale cereale, have given entirely negati\-e 

 results. 



Avena spp. — 41 varieties belonging to 17 species of oats have been 

 examined, and, with the exception of A. bromoides Gouan. and of A. sem- 

 pervirens Yill. which show a marked degree of resistance, all the varieties 

 are shown to be verv' susceptible. The Erysiphe of oats can also develop 

 on Arrhenatherum avenaceum Beauw. The proportion of infection is 14 

 per cent. The parasite cannot however infect barley or wheat. 



The author's work gives many experimental proofs of the existence 



