IS6 



MORPIIOLOG V. 



sporangia, the water should be drawn from under the rover glass 

 with the aid of some bibulous jiajier, like filter paper, placed at the 



edge of the cover glass on 

 the opposite side from the 

 glycerine. As the glycer- 

 ine takes the jjlace of the 

 water around the sjjorangia 

 it draws the water out of 

 the cells of the annulus, 

 just as it took the water 

 out of the cells of the 

 spirogyra as we learned 

 some time ago. As the 

 water is drawn out of these 

 cells there is produced a 

 pressure from without, the 

 atmospheric pressure ujton 

 the glycerine. This causes 

 the walls of these cells of 

 the annulus to bend in- 

 ward, because, as we have 

 already learned, the glycer- 



Section through sorus of Polypodiura vulgare jjig ("Iggg y^Q^ p^gg through 

 showing different stages of sporangium, and one ^ ° 



multiceUular capitate hair. tj^iy walls nearly SO fast 



as tlie water comes out. 



537. Now the structure of the cells of this annulus, as we 

 have seen, is such that the inner walls anci the perpendicular 



Fig.^o.. 

 Section llirougti sorus and sliield-shaped indiisiurn of aspidiuin. 



walls are stout, and consequently they do not bend or collapse 

 when this pressure is brought to bear on the outside of the cells. 



