FERNS. 



I6 3 



The sporangium opens between the lip cells on the front, and the 

 lateral walls of the sporangium are torn directly across. The 

 greater mass of spores are thus held in the upper end of the 

 open sporangium, and when the annulus has nearly doubled on 

 itself it suddenly snaps back again in position. While treating 



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Fig. 138. . 



Dispersion of spores from sporangium of Aspidium acrostichoides, showing different 

 stages in the opening and snapping of the annulus. 



with the glycerine we can see all this movement take place. 

 Each cell of the annulus acts independently, but often they all 

 act in concert. When they do not all act in concert, some of 

 them snap sooner than others, and this causes the annulus to 

 snap in segments. 



