172 
Journal of Agricultural Research 
Vol. XXX, No. 2 
planting the corn upon infection by 
smut. It was believed that ecologic 
information on the prevalence of con- 
idial distribution of the organism might 
be gained by planting certain varieties 
at successive dates during the season. 
The varieties used were Kansas Sun¬ 
flower, Hildreth’s Yellow Dent, Boone 
County White, and Commercial White. 
They were planted, in so far as possible, 
on April 15, May 1 and 15, June 1 and 
15, and July 1, in the years 1915 to 1918 
inclusive. 5 Plantings were made at 
Manhattan and Hays, Kans. The re¬ 
sults seemed to show less infection in 
plantings made on June 15 and July 1 
than in earlier plantings. This might 
be due to the fact that fewer conidia 
occurred at the critical period of in¬ 
fection for these late plantings and that 
environmental conditions were less 
favorable for the development of the 
organism. However, the plantings 
made on July 1 were always only in the 
tasseling stage when the first killing 
frost occurred. This relative imma¬ 
turity of the host would also affect the 
extent to which the plants developed 
visible evidence of infection. Appar¬ 
ently, no evidence can be adduced from 
these results which would warrant con¬ 
clusions of ecologic value. Experi¬ 
ments now being conducted by the 
junior author, in which strains of corn 
homozygous for the character of re¬ 
sistance and susceptibility to smut are 
being used for dates of planting, will no 
doubt give data of value on this point. 
Observations, however (these data are 
summarized by years in the inocula¬ 
tion results in Table I), have indicated 
the increasing prevalence of conidia in 
the cornfield as the season advances. 
It is impossible to escape this increase 
by early planting because of the long 
growing period of the crop. The early 
planting of early-maturing varieties, as 
of sweet corn, might prove of some 
value. 
VARIETAL RESISTANCE 
Experiments to discover possible 
varietal resistance to corn smut were 
made with 25 varieties of maize in the 
three years 1916 to 1918 inclusive. 
Negative results were obtained. None 
of the varieties showed any consistent 
behavior relative to the development of 
smut infection, the differences being 
insignificant and more or less variable. 
Hitchcock and Norton ( 8 ), after an 
extensive series of tests in 1894-1895, 
also concluded that “ there is little 
difference in varieties of corn as to their 
susceptibility to smut.” 
Because of the heterozygous nature 
of the corn plant, these essentially 
negative results might have been an¬ 
ticipated. However, judging from the 
experiments which are being conducted 
at Manhattan at present, it seems 
possible to expect that in many varie¬ 
ties, inbred strains may be secured 
which will vary from complete suscepti¬ 
bility to marked resistance. 
Furthermore, the problem of breed¬ 
ing for resistance may become still 
more complex if specialized forms of 
the organism are found to exist in dif¬ 
ferent localities { 14 )- In such an 
event, it would have a very significant 
bearing on the program of breeding for 
resistance. This phase of the work is 
being investigated by the junior author 
at the present time. 
SUMMARY 
(1) Corn smut is widespread through¬ 
out the Corn Belt and is becoming aD 
important limiting factor in corn pro¬ 
duction in regions of relatively scant 
rainfall. Owing to the nature of corr 
smut infection it has been found im¬ 
possible to control the disease by 
methods commonly applied to other 
cereal smuts. 
(2) A clear conception of the devel¬ 
opment and morphology of the maize 
plant with relation to the occurrence of 
meristem susceptible to infection, is 
requisite to an adequate interpretation 
of the field phenomena which often 
simulate systemic infection. The rudi¬ 
mentary ears of the lower nodes are 
most commonly involved. 
(3) Neither inoculation studies nor 
attempts to shield young plants from 
infection in the field have produced 
evidence to indicate systemic develop¬ 
ment of Ustilago zeae in corn plants in 
the field. Earlier observations bearing 
on this point, therefore, are fully con¬ 
firmed. 
(4) An ecologic study covering four 
crop seasons has indicated that mois¬ 
ture is not a limiting or controlling 
factor in the occurrence of corn smut, 
and that infection does not depend so 
much on the time of the season as on 
the stage of development of the host 
plant. 
(5) The aerial conidia falling upon 
the corn plant do not appear to pro¬ 
duce direct local infection so frequently 
as is indicated by the literature on the 
life history of corn smut. A common 
method of infection is the development 
of a virulent culture in moisture held 
in the axil of a leaf of a young plant. 
* The data at Manhattan, Kans., were obtained from the plots grown by the Department of Ento¬ 
mology of the Kansas Experiment Station. . 
