172 



MORPHOLOGY. 



the sporangium with, we can use dried material, for the move- 

 ments of the sporangia can be well seen in dried material, pro- 

 vided it was collected at about the time the sporangia are mature, 

 that is at maturity, or soon afterward. We take some of the 

 dry sporangia (or we may wash the glycerine off those which we 

 have just studied) and mount them in water, and quickly examine 



Fig. 211. 



Dispersion of spores from sporangium of Aspidium acrostichoides, showing different 

 stages in the opening and snapping of the annulus. 



them with a microscope. We notice that in each cell of the 

 annulus there is a small sphere of some gas. The water which 

 bathes the walls of the annulus is absorbed by some substance 

 inside these cells. This we can see because of the fact that this 

 sphere of gas becomes smaller and smaller until it is only a mere 



