CERTAIN SPECIES OF MUCOR 253 
Spore dilutions were made by transferring some spore material 
with a platinum wire to test tubes containing about twenty 
cubic centimeters of sterile water each. This dilution was then 
sprayed on poured plates, and if the pipettes were fine enough 
and the spores diluted sufficiently, it was always possible to find a 
single spore isolated from the rest. After ten to sixteen hours, 
depending upon the temperature, the plates were examined to 
note whether germination had taken place. For this purpose 
the Petri dish was inverted on the stage of the microscope and 
examined with the low power. If a solitary germinated spore 
was found, the location was marked with a drop of India ink, 
and later the spore, together with a tiny block of agar, was cut 
out by a spear-pointed needle and transferred to a new poured 
plate. The writer has always made it a practice to watch these 
cultures carefully and as soon as possible to make a transfer from 
the edge of the growth, in order to avoid the possibility of con- 
tamination through a neighboring spore delayed in germination. 
This last transfer was usually made within twenty-four hours 
after the spore had been removed. It seems almost unnecessary 
to add that all the cultures used have originated from single spore 
cultures made in the above-described manner. 
3. HERBARIUM MATERIAL 
In addition to depositing living cultures in the Cryptogamic 
Laboratory of the University of Michigan, a series of herbarium 
specimens was also prepared. Inasmuch as the method employed 
may prove useful to others it seems desirable to include it here. 
For the cultures, tall lipless beakers (500 c.c. capacity) were used, 
with a depth of about 3 cm. of bread. If fresh bread was used, 
no water was added, but if dried bread was used, water was 
added until the medium had the humidity of the former. For a 
cover half of a Petri dish was fitted with a thin layer of cotton 
batting, and then the preparations were autoclaved for three or 
four hours at fifteen pounds pressure. 
Pure cultures were employed for inoculation, and then the 
cultures were placed in the dark, in order to secure a symmetrical 
development. The cultures were allowed to stand, not only until 
the maximum growth had taken place, but until the cultures were 
