342 BOTANICAL GAZETTE [NOVEMBER 
dish, lined on all sides with filter paper moistened in distilled water. 
In this way the films were situated in an atmosphere practically 
saturated with water vapor, and each film was under exactly the 
same conditions as regards access of air. This last was a matter of 
great importance, since it was found in the earlier experiments that 
when the preparations were laid on a glass slide, the germination 
was always poorer in the film next to the glass slide, although normal 
germination occurred at or near the edges of the film. 
To save labor, usually 2 or 3 preparations of the same kind were 
placed in a single Petri dish. In the preliminary experiments, 
these dishes had been placed directly in an incubator kept at a 
uniform temperature of 24~-25°C. Even under these circum- 
stances, however, it was realized that the atmospheric condition 
within the Petri dish might not be uniform throughout, for we 
know, of course, that Petri dishes so prepared eventually dry out. 
To obviate this, so far as possible, all the dishes (piled one above the 
other in a column, which rested on 2 or 3 empty dishes, or on an 
inverted stender dish) were stood in one of the halves of a larger 
Petri dish (9 in. diameter) which also was lined with several thick- 
nesses of filter paper and contained a quantity of distilled water. 
The whole was then covered with a bell-jar, likewise lined through- 
out with filter paper, and resting in the larger Petri dish so that 
water was continually being drawn up by the filter paper. In 
this way the atmosphere within the small Petri dishes was kept 
as close as possible to a uniform saturation point throughout each 
dish. 
The whole apparatus was now incubated at 24-25° C., and when 
the germ tubes had grown to the desired length, they were killed 
by dropping a little 4 per cent formalin on the preparations. They 
could then be kept for several days if necessary, or until it was 
convenient to examine them microscopically. For examination 
under the microscope, the preparation was laid very carefully on a 
3 The nature of this entire operation, and the amount of time necessary for its 
completion, made perfect antiseptic precautions impracticable. All that could be 
ome was ‘to have the epparatus scrupulously clean and sterile. As a matter of fact, 
Rhizopus cases more than ro hours, 
would allow bacteria little time for development, and no contamination was ever 
observed in these preparations 
