Aug. is, 1914 
Head Smut of Sorghum and Maize 
345 
were found to be wholly smutted—i. e., producing spores in every head. 
Infected plants of this variety almost always have some normal culms, 
although the number of these varies greatly with the season. Of the 
125 plants examined, 64, or more than 50 per cent, produced one or more 
culms with normal panicles. An infected culm may bear a normal 
head, but this is rare. Usually such a culm bears no seed, and there is 
almost always some degree of abnormality in evidence, the glumes 
becoming elongated and either decolorized or of a greenish hue, 
INFECTION OF NODAL BRANCHES 
Along with these floral changes there usually occurs an abnormal tend¬ 
ency to branch. Indeed, the development of the buds, which occur alter¬ 
nately on opposite sides of the culm at each node, much as in other 
Gramineae (Hackel, 1887, p. 3), is often the only positive evidence of the 
infection, since the resulting branches usually bear sori. This phenome¬ 
non has led Busse (1904, p. 386-392) 1 to consider the infection of a branch 
to take place from hyphge within the node, growing up through the tissue 
of the sheath at the time the bud begins to develop, and he evidently con¬ 
cludes (p. 391) that these nodal buds are not infected until they begin to 
grow out into branches. The histological data given in support of his 
view seem inadequate to establish, beyond a question, his identification 
of smut hyphae in the lesions which sometimes occur in the sheath over 
the swollen buds. The present investigation has shown, too, that these 
buds become infected without reference to their development into branches 
and that there is a peculiar regularity about the infection even when some 
of the branches are missed. 
Forty culms from 15 infected plants of Red Amber sorgo (S. P. I. No. 
17548) grown at Amarillo were dissected and studied for the occurrence 
of the parasite in the nodal buds, and the results are summarized in 
figure 1. The material was killed and fixed with aceto-alcohol (Car- 
noy’s fluid), a mixture of one-third of glacial acetic acid and two-thirds 
of commercial alcohol, for periods varying from 2 to 24 hours. It was 
then rinsed in two or three changes of 70 per cent alcohol and kept in 
this until embedded in paraffin in the laboratory at Washington, D. C. 
All the buds from a single culm were prepared and kept together in one 
vial and were distinguished from each other by cutting them into different 
shapes, which were sketched into a record showing their position on the 
culm. 
The oft-recurring difficulty in definitely differentiating between the 
host and parasite by staining methods was encountered in this work. 
After experimentation it was found that this organism is Gram-positive 
under most conditions, and with a counterstain of eosin in clove oil a very 
1 Busse (1904, p. 391) says, “Ich nehme an, dass die Infektion nicht direkt, sondem auf dem Umwege 
iiber die mit dem Stengel organische verbundene Hauptsprossscheide zu stande kommt.” See also his 
PI. V, figs. 15,18, 18c, and 19. 
