Aug. 1, 1925 
Susceptibility of Onions to Urocystis Oepulae 
283 
regarded as all but immune to smut. Not more than 2 or 3 per cent 
showed smut in the cotyledons, and no smut was seen in any later 
stage. In fact, smut is an entirely negligible factor. This seems to 
be the logical parent species for the breeding of a smut-resistant 
onion by crossing. 
THE RELATION OF UROCYSTIS CEPUL^ TO OTHER SPECIES 
OF UROCYSTIS ON ALLIUM 
As far as the writer is aware, no Urocystis other than Urocystis 
cepulse has ever been found on the cultivated onion. Investigators 
who have found the disease agree as to the remarkable constancy of 
characters of this species so that not even a variety has been sug¬ 
gested. On other species of Allium, however, four other species of 
Urocystis have been found, and from the first description of the 
species up to the present mycologists and pathologists have dis¬ 
cussed the relationship of these other species of Urocystis to U. 
eepulae without reaching any agreement. Some have considered all 
five forms as distinct species, some would unite them all under one 
species, i. e., regard the onion smut fungus as a variety of or identical 
with some of the others. Various other combinations are proposed. 
Not until all of these species have been cultured and studied and 
cross inoculations made on all host species concerned will this ques¬ 
tion be definitely settled; but it is hoped that the inoculation experi¬ 
ments just described and supplemented by examination of exsiccati 
of the pathogenes may contribute something to its solution. Let us 
examine briefly the other four species. 
Urocystis magiea Pass, was named by Passerini from specimens 
which he collected on Allium magicum at Parma, Italy, in 1875, and 
distributed in Rabenhorst’s Fungi europaei as No. 2100 and in von 
Thuemen r s Mycotheca Universalis as No. 228. The writer knows of 
no record that the fungus has ever been collected again on that host 
in Italy or elsewhere. All subsequent literature merely refers to the 
original description or consists of observations on studies of Pas¬ 
serines original collection. It is remarkable that a fungus which was 
so abundant that it could be furnished in plentiful supply for distri¬ 
bution in two exsiccati should never have been collected again. The 
writer had occasion to study specimens of both of these exsiccati in 
the Harvard University herbarium. The long (some of them more 
than an inch) raised sori were on broad flat leaves. A. magicum is 
considered by most phanerogamic authorities as a synonym or a 
variety of A. nigrum L. This latter species, however, does not have 
flat leaves, but linear, terete leaves. Apparently, then, the plant 
on which Passerini collected the parasite was not A , nigrum but 
some other species. The spore balls contained a single spherical, or 
short, oval, brown central cell surrounded by hemispherical accessory 
cells. Only rarely did the writer find two fertile cells in a spore ball, 
and these were not attached by their surfaces, but were held together 
because surrounded by a common layer of sterile cells. In shape, 
color, and arrangement of all parts these spores could not be dis¬ 
tinguished from those of U. cemdae. There is, however, a constant 
difference in size; the spores of U. magiea were larger. Fifty spores 
from each species were measured under, identically the same condi¬ 
tions. The central cell of U. magiea , mounted in lactophenol, meas¬ 
ured 14.27 by 15.55 m as compared with 11.04 by 11.75 /i for U. 
