492 A TEXTBOOK OF THEORETICAL BOTANY 



of the stomium are torn asunder and the annulus, together with part of the 

 sporangium wall, springs back, throwing out the spores. As evaporation 

 continues a point is reached where the cohesion of the water in the cells of 



Archesporial 

 cell 



IVater gland 



Japetum 



Fig. 481. — Dryopteris filix-mas. Stages in the development of a 

 sporangium. {After Kny.) 



the annulus breaks down and air enters the cells. This allows the cells of 

 the annulus to expand again and the sporangium wall snaps back into its 

 original position, thus scattering any spores which still remain in the 

 sporangium. 



