Blakeslee: Mutations in Mucors 279 
SPECIMEN JARS USED IN ISOLATION CULTURES 
The Dwarf true-breeding mutant is shown in the jar at the right, and on the left is shown mutant 
“X,” an unstable mutant reverting to normal type “‘Y.”’ 
The ‘‘Dwarf”’ is eleven days old ‘‘and 
its slowness of growth can be seen in comparison with the seven day old culture on the left. (Fig. 26.) 
tain the proper number of spores as 
determined by examination under the 
microscope. The requisite number of 
spores are transferred with the loop to a 
tube of melted nutrient agar, and the 
agar then poured into an inverted 
specimen jar used as a roll tube shown 
in Fig. 26. By proper manipulation 
under the water tap, the agar is 
hardened, thus holding the spores 
uniformly scattered in a thin layer 
inside the tube. It goes without say- 
ing that the various steps in this process 
should be carried on with regard to the 
precautions necessary to prevent con- 
tamination with foreign spores. By the 
second day the spores have germinated 
and produced mycelial colonies which 
rapidly increase in size and eventually 
cover the available nutrient. Several 
hundred colonies can be readily ob- 
served in a quart sized tube. 
In such an isolation culture just 
described, it is usual to find a few of 
the colonies which differ more or less 
in appearance from the normal growth 
expected for the species. The differ- 
ence may be in the color or compact- 
ness of growth of the mycelium, in the 
lengths of the sporangium stalks, or in 
the size and abundance of the zygo- 
spores which are later produced, or in a 
