Aug. 1, 1925 
Susceptibility of Onions to Urocystis Oepulae 
285 
firming the distinctness of the two species of Urocystis. Another 
collection of a Urocystis on A. oleraceum L. was also referred to this 
same species by Schellenberg. 
ORIGIN OF THE ONION SMUT 
What bearing have the facts set forth in this paper on the problem 
of the origin of onion smut? The writer believes that there are 
good morphological and biological reasons for considering the smut 
fungus as a distinct species from any of the Urocystes found on 
European species of Allium. It should also be pointed out in this 
connection that even if it should be found that some one of the 
European species named in recent years was identical with Urocystis 
cepulae, this would not indicate a European origin for the disease. 
It seems to the writer that it would be much more logical in that 
case to conclude that the fungus was first on onion and passed from 
the onion over to the other species where it was collected. In fact, 
in view of the wide host range which the writer has demonstrated 
for the onion smut organism, it would seem remarkable if it should 
not be taken some time by some collector on another species. Dur¬ 
ing the 50 years that it has been in Europe it has had abundant 
opportunity to spread to other hosts. 
In brief, in the writer’s opinion, there is not the least evidence 
that the disease is of Old World origin. On the contrary, there is 
excellent circumstantial evidence that it did not exist there on any 
species previous to its discovery in America. Onions have been 
grown and used by every civilized people in the Old World at least 
since the building of the pyramids. In all that time onions certainly 
must have come in contact with every disease which occurred on 
other species of Allium indigenous to the countries where they grew. 
Smut is by no means an inconspicuous disease, and if it had been 
present in the Old World it very likely would have been mentioned 
before 1872. 
Some of the susceptible species mentioned in this paper are native 
to the New World, and probably further search will add to the list 
of our indigenous susceptible ones. Some one or more of these 
was probably the original host. Possibly it was a native of the 
far West in this country, like the susceptible Allium nevadense. 
For many years ^fter the onion was brought to America smut seems 
to have been unknown. The writer offers the theory that as the 
frontier of civilization advanced into the West, taking along with it 
the onion, the onion came into contact with the organism in its 
native home, and that the spores could easily have been taken back 
to New England in the natural course of commerce, with the result 
that the disease first became prominent in a great intensive onion 
center, such as eastern Massachusetts was at that time, rather than 
in the isolated gardens of the pioneers. It may be significant that 
smut first appeared within the next decade after the California gold 
rush of 1849. 
SUMMARY 
None of the 54 varieties of cultivated onions tested showed any 
considerable resistance to smut. 
Out of 39 species of Allium tested, 8 seemed to be immune, and 
31 showed varying degrees of susceptibility. 
