Pethybridge — Observations on Phytophthora erijthroseptica. 195 



whole plant to prove with absolute certainty that the same fungus is the actual 

 cause of the symptoms of disease observable. 



The circumstantial evidence is, however, strong. Certainly the symptoms 

 described do not at all resemble those of the blight or of the Stalk 

 (Sclerotium) Disease, two of the most prevalent diseases on the Clifdeu plots. 

 It might be argued that the affected plants described were cases of Black Stalk 

 Rot, supplemented by the subsequent saprophytic invasion of P. erythroseptica. 

 This is decidedly improbable, for this fungus has been proved to be a 

 virulent parasite of the potato, destroying both living tubers and stalks 

 when inoculated into them. Further, had the plants first been attacked 

 by Black Stalk Rot, it is practically certain that their diseased condition 

 would have been observed many weeks earlier than was the case. Lastly, 

 the Black Stalk Rot disease has been eliminated almost completely from 

 the plots at Clifden, so that there would not have been a sufficient number 

 of such plants present in the plots to account for the observed prevalence 

 of tlie Pink-Rot Wilt. 



The actual details as to how the primary infection of the plant from the 

 soil occurs are not yet known ; but it is probable that the germ-tubes of 

 the zoospores, conidia, and oospores possess the power of penetrating the 

 epidermis of some portion or portions of the underground parts of the plant. 

 That these germ-tubes are incapable of penetrating the superficial tissue 

 when it consists of corky periderm seems to be probable from the fact that 

 unwounded tubers invaded other than directly through the rhizome are of 

 the greatest possible rarity.' Further, since healthy tubers, when pitted in 

 close contact with cut or damaged diseased ones, do not become diseased, it 

 would appear that the mycelium of the fungus is incapable of penetrating 

 through the skin of the tuber. This is rendered all the more probable from 

 the fact that the fungus does not grow out through the skin of affected 

 tubers so long as the latter remains intact and unbroken. 



With regard to the occurrence of the disease it has been seen up to the 

 present only in Ireland ; but there is no reason to suppose that it is strictly 

 limited to this country. Particularly in districts where potatoes are cultivated 

 too frequently in the same ground, it is likely that careful search will reveal 

 its presence. It is on land of such a character that the losses caused by it 

 are most serious, although it has been met with to some extent in parts of the 

 country where better methods of farming prevail. 



On poor reclaimed bog-soil at Clifden, Co. Galway, which liad borne 



1 This has been observed in only two cases, and even in these the fungus might have gained an 

 entry through minute wounds, too small to be seen easily, or which had, subsequent to infection, 

 become more or less obliterated. 



SCIENT. PEOC. R.D.S., VOL, XIV., NO. X. 2 G 



