124 
EtroLtocy oF Foot-rot 
EVIDENCES OF ETIOLOGICAL RELATION OF H. NO. 1 
Constant Presence of the Pathogene 
In all cases of American foot-rot of wheat that have come under my 
observation the rotten basal portion of the shoot bore and was to a large 
extent occupied by a mycelium, which grew luxuriantly within the wheat 
tissue though very sparingly upon its surface, coursing lengthwise within 
the diseased cells. This mycelium was hyaline, septate, vacuolate, irregular 
in thickness, and, in short, agreed in all characters with those of H. No. 1 
when growing in rotting wheat-tissue (page 105). 
Absence of other Constant Parasites 
No other organism which might be considered as a possible parasite was 
present in any large number of cases in or on the wheat tissue. Amebae 
and nematodes were present in great numbers in the soil, but appeared to 
bear no relation to the rot of the wheat. Various fungi, as Fusarium (two 
species), Rhizoctonia, Epicoccum, Alternaria, were occasionally found on 
the roots or stems, but each only rarely, in a fraction of 1% of the cases, 
and with no evidence of etiological relation to the rot of the stem. 
Identity of Pathogene proved by Culture 
Very numerous isolations were made by taking bits of tissue (1) from 
diseased sheaths, (2} from diseased stem-lesions, and (3) by stripping away 
the sheath, disinfecting the remaining surface with mercuric chloride and 
taking out diseased bits, with precautions against contamination. All 
such diseased bits were laid on the surface of corn-meal agar plates. Hun- 
dreds of these were made, with the result that in practically every instance 
the diseased bit gave rise to Helminthosporium conidia in general aspect 
like those of H. No. 1. Other organisms, as mentioned, occasionally 
occurred on these plates, but in only a small per cent. of instances. It 
seems entirely conclusive that the mycelium constantly found in the rotting 
basal portion of the diseased wheat-stems is that of a Helminthosporium. 
Evidence of Infectiousness 
Several bags of soil that bore diseased wheat in 1919, near Granite 
City, Illinois, were brought into our greenhouse in July, 1919. In this soil 
was planted ‘‘Sultzer Pride’ wheat, and the planting kept liberally watered. 
At the end of some weeks the plants were removed, and on examination all 
