Jan. 15,1925 
Ecological Relations of the Smut of Maize 
169 
of qarrot decoction which were allowed 
to incubate at 23° to 25° C. for two 
or three days, until the culture ap¬ 
peared turbid and sometimes covered 
with a thin scum of aerial conidia. 
These liquid cultures were used to 
inoculate young plants either by pour¬ 
ing them into the leaf axils, or by in¬ 
jecting them into the region of the 
growing point (6 or 10 inches from the 
ground in plants 12 to 18 inches high) 
by the use of a hypodermic needle. 
Of the three isolations, all of which 
were used in numerous inoculations, 
No. L 44c alone gave positive results, 
producing smut in almost every trial. 
Plate 2 well illustrates its virulence. 
Isolations Nos. 6c, 79, and 88 were 
made in 1917 and may be taken as 
typical examples of virulent cultures. 
Continuously growing them on artificial 
media did not seem to reduce their 
virulence when used for inoculation. 
Culture No. 6c was isolated as 
described for No. L 44c, from the top¬ 
most leaf axil of a plant 5 inches tall. 
Three isolations taken from this same 
agar plate proved virulent. The re¬ 
sults of an inoculation with “6c” are 
shown in Plate 7, A, B, and C. 
Culture No. 79 was isolated by using 
photographer's porcelain developing 
trays containing a small quantity of 
distilled water and having a surface 
5H by 8 inches. These were exposed 
for 16 hours in the cornfield. Of the 
12 cc. of liquid recovered from the 
water plate, one-third was used in 
pouring the agar plate for isolations. 
Numerous colonies appeared in the 
plate. One was isolated and proved 
virulent in a number of trials (pi. 7, C). 
Culture No. 88 was isolated the 
latter part of July from the axil of the 
ninth leaf of a fully developed corn 
plant. This proved virulent in several 
trials in both 1917 and 1918 (pi. 3, E). 
From Table I, it will be noted that 
the isolation of cultures which seemed 
to be morphologically identical with 
those of Ustilago zeae was accomplished 
frequently and with little difficulty. 
In many cases, however, there remained 
some doubt as to the identity of such 
cultures, because the smuts in artificial 
culture or as young colonies closely 
resemble numerous yeasts and other 
somewhat similar organisms. The fact 
that many of the cultures proved viru¬ 
lently pathogenic leads to the belief 
that others also may have been pure 
cultures of U . zeae, although no infec¬ 
tions were obtained. Such an assump¬ 
tion is supported by the coincident 
failure of virulence in known cultures 
originally made from a single chlamy- 
dospore of U. zeae. The plants used 
13950—25f-6 
for inoculation were grown from seed 
of • open-pollinated ears. This un¬ 
doubtedly could explain part of the 
irregularities obtained in such inocu¬ 
lations, and is supported by results of 
experiments now being conducted in 
Kansas to determine relative resist¬ 
ance of inbred strains of corn to smut. 
The nature of the infection, also is 
pertinent in such cases as those noted 
by Pammel and Stewart if we may but 
alter their statement to read, “where 
one smut boil made its appearance on 
the upper nodes others appeared 
farther down.” In other words, it 
would seem that such infections fre¬ 
quently arise from one and the same 
contamination of axillary moisture by 
Ustilago zeae at a relatively early period 
in the plant's development. This 
axillary culture then spreads by running 
down into the lower axils. This view 
of axillary contamination has appealed 
also to Arthur and Stuart (2), except 
that they do not trace the several galls 
to the same contamination, nor have 
they evidence that U. zeae ever was 
present in the leaf axils. The writers 
have produced such infections by arti¬ 
ficial inoculation, an example of which 
is seen in Plate 2, A. 
At the beginning of these investiga¬ 
tions the point which appealed to the 
writers as most pertinent to the prob¬ 
lem of fungicidal control was the prob¬ 
ability that aerial conidia falling upon 
the corn plant produce direct local in¬ 
fection only in some instances. Sus¬ 
ceptible tissues of the host are seldom 
exposed to direct attack, except per¬ 
haps by some injury (7), so that in the 
normal course of events an interval 
must occur between the contact of the 
conidium with the host and actual in¬ 
fection of the tissues. In this respect 
Ustilago zeae may be considered as dis¬ 
tinct from other more highly specialized 
parasites among the cereal smuts, most 
of these being capable of infecting only 
the very young seedlings. The latter 
necessarily have to enter their hosts in 
the seedling stage if they are to infect 
at all. 
Corn smut, on the other hand, may 
be considered frequently pseudosyste- 
mic in its attack, as it appears to exist 
on the host rather than in it prior to 
the development of the disease in its 
most typical form in the nodal buds or 
ears. This fact is of interest in view 
of the positive statement of Arthur 
and Stuart (2) that fungicidal sprays 
gave definite indication of control. 
The writers, therefore, have attempted 
similar treatment with several varia¬ 
tions, not so much with the idea of any 
immediate practical importance which 
