254 MORPHOLOGY. 



is termed the annulus, which means a little ring. While this 

 is not a complete ring, in some other ferns the ring is nearly 

 complete. 



534. In the front of the sporangium is another peculiar group 



Fig. 

 Rhizome of sensitive fern (Onoclea sensibilis). 



of cells. Two of the longer ones resemble the lips of some crea- 

 ture, and since the sporangium opens between them they are 

 sometimes termed the lip cells. These lip cells are connected with 

 the upper end of the annulus on one 

 side and with the upper end of the stalk 

 on the other side by thin -walled cells, 

 which may be termed connective cells, 

 since they hold each lip cell to its part 

 of the opening sporangium. The cells 

 on the side of the sporangium are also 

 thin-walled. If we now examine a 

 sporangium from the back, or dorsal 

 Under side of pinna of Aspidium edge as we say, it will appear as in the 



spinulosum showing fruit dots , , ~. 



(sori). left-hand figure. Here we can see 



how very prominent the annulus is. It projects beyond the 

 surface of the other cells of the sporangium. The spores are 

 contained inside this case. 



