Minnesota Plant Life. 71 



exposing the third and innermost skin which remains intact. 

 Tlie hole enlarges so that there comes a moment when the in- 

 ner skin lies like a base ball in a tea cup, surrounded by the two 

 outer skins which have taken a vase-like form. Very suddenly 

 the middle skin separates from the outer skin everywhere ex- 

 cept at the edges and inverts itself with explosive force. It is 

 as if the lining of a porcelain kettle should turn inside out. By 

 this means the little ball at the centre may be projected several 

 inches into the air as if shot out of some tiny catapult. In this 

 way the whole mass of spores enclosed in the inner skin is 

 thrown to some distance from the point where the parent plant 

 developed, thus adding to the favorable chances of the species 

 in distribution. 



