170 BOTANICAL GAZETTE [SEPTEMBER 
they are scattered through the whole culture. They should not 
be least abundant in the center, however, and a very few isolated 
zygospores at some distance from the line of contact make one 
suspicious of possible infection and demand a repetition of the 
culture. 
In the study of incompleted sexual reactions such as are found 
in ‘‘imperfect hybridization,” greater care must be exercised than in 
the observation of zygospores, since the cultures have not been 
sterilized, and infection may take place in an early examination of 
the dishes and be the cause of the sexual reactions seen when the 
cultures are looked at later. At first glass plates were used to 
cover the cultures, to prevent the delicate filaments from drying 
and collapsing while they were being examined. This entailed 
cleaning and sterilizing the plates in alcohol and afterwards drying 
them, and consumed more time than the procedure finally adopted. 
By this method a-stack was placed on a sheet of wet blotting paper 
and covered with a crystallizing dish lined with moist paper,’ thus 
forming a humidor for the cultures. The stage of the binocular 
microscope was covered by several layers of wet blotting paper 
perforated to match the opening in the stage for the entrance of 
light. A collar of moistened blotting paper formed a moist chamber 
with the wet paper on the stage and allowed the examination of 
a culture to continue fér some time without collapse of the hyphae. 
The cover was removed from the stack in the humidor formed by 
the crystallizing dish and placed upside down on the table. The 
bottom of the first culture dish was swabbed with a pledget ‘of 
cotton soaked with alcohol before being put in the moist chamber 
formed on the stage of the binocular, and after being examined was 
placed upside down on the inverted cover. The second,. third, 
and fourth cultures were treated in a similar manner, except that 
the bottom of the fourth culture, which had not been in contact 
with any culture below it, was not treated with alcohol. After 
the last dish had been removed from the humidor and examined, 
it formed the last member of an inverted stack, and a new stack 
was placed in the humidor ready for examination. From time. to 
time it was found necessary to re-wet or renew the blotting paper 
on the binocular. The paper on the stage is theoretically capable 
