226 BOTANICAL GAZETTE [SEPTEMBER 
stout Manila twine. As the membrane dries it adheres tightly to the 
flange, and since it contracts somewhat on drying, it becomes stretched 

& 
Fic. 1.—Celloidin film on a dish of mercury; the edges show the characteristic 
appearance at time when it is “ripe.”’ 

2.—Different Stages in the formation of celloidin membranes: A, membrane 
Fr 
after being placed over the bulb of a thistle tube; B, showing how the film adheres 
to the flang 
e; C, after tying the membrane on the thistle tube; D, a double membrane. 
as taut as the head of a drum (fig. 2, B). The ends of the twine are then 
cut off and the part of the film which extends more than a quarter of an 
