Pethybuidgio and Mvrfb.\' —Bacterial Dtsease'of the Potato. 7 



of rod-like shape, of very varying length, very frequently arranged in pairs, 

 and possessing several flagella. It is very actively motile, and produces rapid 

 liquefaction in neiitral or slightly alkaline gelatine media, but none in those 

 which are acid. Its most striking characteristic is its power of destroying 

 rapidly the Li^dug tissues of healthy potato-tubers, producmg in them a brown 

 discolouration. Appel maintains that the potato-plant may become attacked 

 directly fi'om the soU, but is also con\n[nced that the spread of the disease is 

 as much or more due to the planting of affected tubers. A more popular 

 and succinct, but withal scientific, account of the disease was published (5) 

 in leaflet form, with a coloured illustration, in August, 1904. 



Since the appearance of Appel's account, several workers in different 

 countries claim to have observed the same disease and the same organism ; but 

 in most cases the absence of published details renders it somewhat difficult 

 to judge whether the organisms in cj^uestion really were identical with 

 B. phytophthorus or not. Delacroix (12), writing in 1906, states that, although 

 up to two years pre\iously nothing was known of this disease or this organism 

 in France, he has now had cases of it, although the disease is by no means 

 widespread in that coimtry. It differs from the " brunissure," caused by B. 

 solanincola in appearing much earlier in the season ; and the organism differs 

 from that one in that B. iJhijtopMhorus liquefies gelatine ; whereas B. solanin- 

 cola does not. Nevertheless Delacroix states that the similarity in the general 

 characters of the two diseased is so marked that the only satisfactory way of 

 distinguishing between them is that of isolating the causative organisms. 



Johnson (22), in 1906, states that he got clear evidence of the existence of 

 B. phytoplithorus as a general cause of " yeUow-blight," " black-leg," and 

 potato-tuber rot in Ireland. Unfortunately the evidence is not produced ; and 

 it is impossible, therefore, to be sure in the matter. If this organism exists in 

 this country in addition to the three others (mentioned on p. 5), which 

 this author states he has foimd here, then Ireland is indeed unfortunate in 

 possessing more than her fair share of the world's varieties of bacteria 

 pathogenic to the potato ! Some doubt may fairly be said to exist as to the 

 correctness of Johnson's diagnosis in the last case from a consideration of the 

 single infection experiment described and figured. A potato-plant in a pot 

 was inoculated (whether with a pure culture or with raw, diseased tissue is 

 not stated) and complete wilting of the inoculated stalk occurred within 

 twenty-four hours. Such rapidity of action would be extraordinary in the case 

 of B. phytophthorus, which, as a rule, only exliibits its pathogenicity under 

 such conditions after a considerable lapse of time, and not by a sudden 

 wiltmg. Working with an organism which is certainly closely allied to the one 

 named, we have found that under ordinarv outdoor summer conditions a 



