SORGHUM SMUTS AND VARIETAL RESISTANCE 5 
and 2 to 4 millimeters in diameter (Pis. II and III) . The wall of this 
structure consists of a rather thick grayish brown membrane, com- 
posed mainly of hyaline, oblong to subspherical fungous cells 7 to 9 
ix in diameter. The wall incloses the smut spores which fill the interior 
and surround the central columella, consisting mainly of the rem- 
nants of fibrovascular bundles. The membrane breaks more or 
less irregularly when mechanically injured and allows the spores 
to escape. This commonly takes place in threshing operations and 
results in the contamination of the grain. 
The spores, morphologically chlamydospores, are spherical or 
subspherical, rather thick walled, smooth, and 5 to 9 \x in diameter, 
averaging about 6 /*. In mass the spores are dark brown, but singly 
they are olive brown in color. They may retain their viability for a 
long period. 
The germination of the spores has been described by Brefeld {12), 
Norton (80), Clinton (22), Kulkarni (63), Butler (21), and others. 
They germinate readily in water and in one type of germination give 
rise to a typical promycelium of three to four cells, which buds off 
sporidia laterally and from the apex. The sporidia are spindle 
shaped, 10 to 12.5 by 2 to 3 /x. Clamp connections and buckle joints 
occur. In the other type of germination the spore does not give rise 
to a typical promycelium, but a branching germ tube arises from the 
spore. Various intermediate types may occur. In various nutrient 
solutions a more vigorous germination takes place, giving rise to 
typical promycelia with sporidia, and the latter multiply rapidly by a 
process of budding. 
Clinton (22) was one of the first investigators to demonstrate the 
probability of seedling infection by means of seed-borne spores. He 
planted inoculated seed as well as seed from a smutted crop and 
obtained a relatively high percentage of smutted plants. He also 
inoculated seedlings before they emerged from the soil and obtained 
a slight amount of infection. Kellerman (52, 54) inoculated sorgo 
and broomcorn seed with spores obtained from sorgo and obtained 
about 19 per cent of infection in the sorgo and 49 per cent in broom- 
corn. The significance of seed-borne spores in the development of 
covered kernel smut is amply proved by the work of Kulkarni (63) 
and others. Infection appears to occur between the time of the ger- 
mination of the seed and the appearance of the young seedlings above 
ground. The germ tubes which develop either from the promy- 
celium or the sporidia penetrate the young shoot of the host and give 
rise to the mycelium in the growing plant. Reed (97) abstracted 
the data presented in this bulletin. He discussed briefly the relative 
resistance of the various groups of sorghums to the covered and loose- 
kernel smuts, reviewed* the literature dealing with these smuts, and 
gave descriptions of SphacelotJieca sorglii and SpJiacelotheca cruenta 
as contained herein. He also presented data for 1922, showing the 
resistance of sorghums to these smuts at the Brooklyn Botanic 
Garden during that year. 
LOOSE KERNEL SMUT 
The loose kernel smut (SphacelotJieca cruenta (Kuhn) Potter) was 
first described in 1872 by Kuhn (59) and named by him Ustilago 
cruenta Kuhn. Winter (120) recorded it in Germany, Schroeter (104) 
