139 
of the affected leaf, and also rotting without spotting, resulted. On the 
leaves in the humid air of the rag doll occasional spontaneous infections 
were noticed. In such cases the infection rapidly spread, involving nearly 
all of the leaf, which first turned pale, then very slightly brown. Aerial 
mycelium and conidia were profuse over the diseased portion. 
SUMMARY CONCERNING ETIOLOGY OF FOOT-ROT 
The evidence is conclusive that Helminthosporium is the cause of 
the basal rot of the wheat-stems. It is the only parasite constantly 
present, and has been repeatedly, and by many methods, proved capable of 
causing such rot. This conclusion is in accord with the findings of Beck- 
with (14), who as early as 1911 showed that Helminthosporium is a very 
common parasite within the tissue of wheat-plants. Bakke (6) in 1912 
reported that when conidia of H. teres were placed on barley seeds, 
“At the end of two weeks’ time there were not over seven seedlings to 
the row [originally there were twenty-five]. The roots were not in any 
sense indicative of a healthy state of growth.’’ Oats and fescue-grass 
were not susceptible. A seedling blight of wheat observed since 1910 has 
been described by Stakman (113) in Minnesota, where in 1918-19 it became 
seriously injurious. The symptoms include dwarfing, foot-rot, and root- 
rot. The disease appears to be closely like, if not quite identical with, 
the one which is the subject of this paper. She proves conclusively that 
the cause is a Helminthosporium. A foot-rot of wheat due to a Hel- 
minthosporium having quite different morphological characters is also 
known in Sudan (see No. 46, page 184). 
Certain of Ravn’s experiments (91) conducted by inoculating seeds 
on wet filter-paper in a Petri dish, gave conditions much like those in 
the rag dolls. He makes no mention, however, of infection of the sheath 
nor of the occurrence of rotting of the basal region. 
II. Evidence and Discussion of the Occurrence of 
Saltation within the Genus Helminthosporium 
INTRODUCTORY 
Early in my study of this Helminthosporium of foot-rot of wheat 
(herein designated as H. No. 1) it was noted that occasionally certain sectors 
of a colony growing on an agar plate differed more or less from the rest of 
the colony (Pl. XXII, 5; Pl. XXIII,1). This phenomenon is of rather 
common occurrence in work involving Petri-dish cultures of either fungi or 
bacteria, and little significance was at first attached to it; but later, when 
