THE SPHAEROBOLUS GUN 319 



membrane, it is the tendency of the upper part to increase in surface 

 area opposed by the tendency of the lower part to decrease in surface 

 area that eventually leads to a condition of stress and strain being 

 set up in the whole, with a climax that results in eversion. This 

 climax arrives when the rim of the cup has been bent outwards 

 sufficiently to allow the main part of the everting membranes to 

 become broadly U-shaped in form. 



The general mode of action of the dual everting membrane of 

 Sphaerobolus can be illustrated very simply by means of a working 

 model consisting of a strip of writing paper, 6x2 inches, and a 

 small coin for a projectile. One places the coin in the middle of 

 the piece of paper. Then, holding the two ends of the paper with 

 a finger and thumb of each hand, one pushes the two ends toward 

 one another until the centre part of the paper is broadly U-shaped. 

 The coin now lies at the bottom of the U- Then one bends the 

 ends of the paper more and more outwards until, suddenly, eversion 

 of the central U-shaped part of the paper takes place and the coin 

 is shot some 6-8 inches upwards into the air. The same experiment 

 can be performed with more effect with a thin strip of cardboard 

 or mica. Using a sheet of cardboard, 8 x 10 inches, taken from 

 the back of a writing-pad, I was able to shoot a five-cent or ten-cent 

 piece to a height of over 6 feet and to make it hit the ceiling of my 

 office. 



The expansion of the palisade layer is caused by the lateral 

 swelling of the individual palisade cells, and this swelling appears to 

 be due to increasing turgescence. Both Miss Walker and I, by 

 means of microchemical tests with iodine, have observed that the 

 palisade cells of unopened fruit-bodies are densely filled with glyco- 

 gen and that this glycogen disappears during the few hours inter- 

 vening between the opening of the fruit-body and the discharge of 

 the projectile. That the glycogen is converted into sugar was to 

 be expected, and actual evidence that this supposition is correct 

 has been obtained by Miss Walker assisted by Miss Andersen. 1 

 These investigators tested the palisade layer for sugars with 

 Fliickiger's reaction and the phenylhydrazine reaction and found 



1 Leva B. Walker and Emma N. Andersen, " Relation of Glycogen to Spore- 

 ejection," Mycologia, Vol. XVII, 1925, pp. 154-159. 



