MUTATIONS IN MUCORS' 
ALBERT F. BLAKESLEE 
Station for Experimental Evolution, Cold Spring Harbor, N. Y. 
HE theory of mutations has 
played an increasing réle in 
experimental evolution since its 
enunciation some twenty years ago. 
Sudden germinal changes, large or 
small in amount, have been the basis 
of perhaps the most fundamental work 
in modern genetics. It is natural that 
mutations should have been first sought 
for and found primarily in higher 
organisms, and in connection with the 
sexual reproduction which is charac- 
teristic of such forms. It became 
evident later that mutations could not 
be confined to cells associated with 
sexual reproduction, but, as shown by 
the somatic mutations” involved in 
bud sports in plants, and in similar less 
common phenomena in animals, they 
may occur in cells in which sexual 
processes are not involved. They have 
been found in lowly organized plants 
and animals in which nonsexual repro- 
duction is the rule or in which sexual 
reproduction is not known to occur. 
The mucors are a fungous group in 
which multiplication is brought about 
chiefly by nonsexual spores produced 
in sporangia. Sexually formed zygo- 
spores are rarely found in most forms. 
There are two main groups as regards 
their sexual reproduction :—dioecious 
forms and hermaphrodites. The sexual 
races of the dioecious forms are in the 
main similar in appearance, and the 
uniting sex cells or gametes are appar- 
ently morphologically equivalent. For 
this reason, the terms plus and minus 
have been applied to their opposite 
sexes instead of the terms male and 
female used in reference to the mor- 
phologically distinct sexes in higher 
forms. In many cases it has been 
possible to obtain a sexual reaction, 
called “imperfect hybridization,’ be- 
tween plus and minus races of different 
species. This imperfect hybridization 
reaction has also been used in testing 
the sexual tendencies of hermaphro- 
dites and their mutants. 
It is in a species of the hermaphro- 
dites (Mucor genevensis) that the 
mutations discussed in the present 
paper have been found. Races of this 
species from three different sources 
have been kept running in vegetatively 
propagated pure lines for 19 years. 
The species was studied in 1913 with 
the hope of inducing germinal changes 
by subjecting its vegetative growth or 
mycelium to various physical and 
chemical stimuli. Before concluding 
that any variation found after sub- 
jecting the mycelium to a given stimu- 
lus was in fact brought about by this 
stimulus, it was necessary to discover 
what, if any, variations the fungus 
would produce under normal condi- 
tions. So many variants were dis- 
covered, however, in this preliminary 
study, where no special stimuli were 
applied, that extensive investigations 
have not yet been attempted as to the 
range of variations under abnormal 
conditions. 
METHOD OF GROWING MUCORS 
The method of growing these mucors 
is relatively simple. To be sure that 
there is no doubt as to the purity of the 
stock with which one starts, it is de- 
sirable to obtain a culture from a single 
vegetative spore. This  single-spore 
culture is grown in a test tube and, in 
addition to slow-germinating zygo- 
spores, produces numerous sporangia 
containing thousands of nonsexual 
spores. These sporangiospores are 
mixed with water and the spore mixture 
diluted until a platinum loop will con- 
_ ‘A preliminary report of mutations in mucors was given in Year Book of the Carnegie Institu- 
tion of Washington XII, 104-105, 1913 and presented before the Amer. Soc. of Naturalists, 
Dec., 1914. 
