1921] BLAKESLEE, WELCH, & CARTLEDGE—MUCORS 167 
being written on the culture. This alcohol bath helps to sterilize 
not only the needle but also the base of the needle holder, which 
cannot readily be flamed, but which may carry spores from the 
test tube cultures. The alcohol was burned off and the needle 
flamed before a new inoculation was made. A layer of shot will 
be found convenient to weight the jar of alcohol and to receive 
the point of the needle. It is a rule of the laboratory never to lay 
a test tube down from which a transfer is being made until the 
label is written on the new culture. 
The first race to be tested was inoculated in a streak at the 
left and at the right respectively of the first and second culture 
dishes in the stack. Similarly the second race was streaked at 
the left of the third dish and at the right of the fourth dish. In 
like manner other stacks were inoculated with the remaining races to 
be tested, so that finally a series of stacks was secured with two 
of the dishes streaked with one race and two dishes with another 
race. They were then ready to be planted with the testers, which 
are most conveniently a pair of races of opposite sex. In such a 
case, the plus was streaked on the right of the first and third culture 
dishes of each stack, and the minus on the left of the second and 
fourth dishes. Each dish, therefore, contained a tester and a 
race to be tested, and each stack accordingly completely tested 
two races. An advantage in choosing a plus and a minus race as 
the two testers in a series was that they could be planted together 
as controls for the production of zygospores. They may be 
grown in duplicate, and a pair of dishes with nutrient but without 
inoculations may complete the control stack and give evidence 
of the amount of infection to which the cultures are liable. In 
inoculating the testers a larger amount of spore material was rolled 
up on the needle, which sufficed without renewal for the inocula- 
tion of 30 or 4o dishes. With practice the process of inoculation 
could be carried on with relative rapidity. In inoculating a culture 
with more than a single race, the needle should be kept on its own 
side, to decrease the likelihood of spores falling upon a part of the 
substratum reserved for another race. 
When “imperfect hybridization” was expected, the tester and 
the race to be tested were streaked so that the lines of inoculation 
formed a V instead of running parallel. In consequence, the two 
