A TEXT-BOOK OF BOTANY. 



tuting what is known as the ANNULUS (Fig. 53, n). The form of 

 the annulus determines the manner of dehiscence of the sporangia, 

 which occurs on drying. The spores are ejected with consider- 



FIG. 53. Male fern [Dryopteris (Aspidium or Nephrodium) Filix-mas]. A, portion 

 of leaflet showing a number of more or less reniform sori near the mid-vein; B. transverse 

 section through a ripe sorus showing clusters of stalked sporangia, which are covered by 

 the indusium (i), an outgrowth of the leaflet; C, a closed but ripe sporangium showing the 

 annulus or ring (n), and the irregular-shaped spores within; D, showing the manner of 

 opening of the mature sporangium and the dispersal of the spores; E, two spores much 

 magnified. After Dodel-Port. 



able force (Fig. 53, D). They (Fig. 53, E; Fig. 57) are either 

 bilateral or tetrahedral and require a short period to elapse before 

 they germinate. They retain their vitality for a long time, except 

 those which are green, i.e., contain chlorophyll. The spores are 



