280 
number of other characters, but most 
commonly in the reduced size of the 
colonies. The aberrant colonies may 
be transferred uncontaminated to test 
tubes before the spores are produced 
or their spores may be used in making 
a new isolation in a second roll tube. 
In all, somewhat over 38,000 colonies 
from individual sporangiospores have 
been inspected and a relatively large 
number of variants of different degrees 
of distinctness have been obtained. 
The history of nearly all of these 
mutants is similar in that the mutants 
tend eventually to revert to the normal 
type. Two, however, have seemed 
more stable than the rest. 
A FIXED DWARF MUTANT FOUND 
A mutant which can conveniently 
be called the ‘‘Dwarf’’ was found in 
March, 1913 in an isolation of spores 
from a single test tube culture of the 
normal stock. Among 1015 individ- 
uals, a single colony was noticeably 
smaller than the rest and different 
from its neighbors in the density of its 
mycelium and the ragged edges of its 
growth. Transfers of the mycelium to 
test tubes and continued cultivation 
for nearly seven years on a variety of 
media in gross and isolation cultures 
make it apparent that the mutant 
is fixed and constant. Its charac- 
teristic appearance, in an isolation 
culture, is shown in the right hand tube 
in Fig. 26. This is eleven days old, 
and its slowness of growth can be seen 
in comparison with the seven day old 
culture on the left, especially with the 
lower colony marked ‘‘X”’ which had 
more room for extension than its 
neighbors. Perhaps the most striking 
peculiarity of the Dwarf is its lack of 
definitely formed spores characteristic 
of the group and found in all our other 
mutants. The mycelium is granular 
and readily breaks up into bits of the 
mycelium, so that isolation cultures 
from these fragments can be made, but 
no sporangia have ever been observed. 
The difference in size of the colonies 
in the tube photographed may be due 
to a difference in the size of the frag- 
ments from which they grew. The 
The Journal of Heredity 
granular nature of its vegetative 
growth is merely a more pronounced 
expression of a tendency already pres- 
ent in the parent stock especially when 
grown in sugar solutions. Like the 
normal stock, the Dwarf also is able to 
take active part in alcoholic fermenta- 
tion. 
Zygospores, normally characteristic 
of this hermaphroditic species, are also 
entirely lacking, as might be expected 
from so weak a growth. For the same 
reason perhaps, it fails to give any 
sexual reaction with plus and minus 
races of a test dioecious species. The 
inhibiting effect upon growth of adja- 
cent colonies may be noted in the photo- 
graph by their flattened outlines and 
the clear space between, where other- 
wise they would grow into contact. 
Instances where colonies seem to over- 
lap are due to colonies showing through 
from the other side of the tube. 
A MUTANT FROM A COLONY LACKING 
ZYGOSPORES 
The second mutant to be considered 
which appears to breed true was found 
February 22, 1913 in a two weeks old 
isolation culture of 265 colonies. This 
single colony, labelled Ai, entirely 
lacked zygospores which thickly dotted 
all the other colonies in the series. It 
was freed from its zygosporic neighbors, 
with which its sporangia were inter- 
mingled, by streaking its spores on 
nutrient agar in a Petri dish culture. 
Some of the colonies produced zygo- 
spores and were considered to be from 
spores of other adjacent colonies. 
Some were entirely free from !zygo- 
spores. One of the latter was trans- 
ferred to a tube culture while young 
and labelled A2. From A2 an isolation 
culture was made on March 7, and pro- 
duced 4631 colonies, all of which 
lacked zygospores. One of these colo- 
nies (A3) was used in making another 
isolation culture and yielded 24 colonies 
again, all without zygospores. The 
mutitant race has been continued in 
test tube culture since 1913 and at the 
present writing has reached the 16th 
nonsexual generation. Tube A16 is dis- 
tinctly different from other races of 
