102 
Cavers. — On the Structure and 
though appearing to be sessile at the anterior margin of the thallus (PL VII, 
Fig. 32) ; it is protected in front by the overlapping ventral scales, behind 
and at the sides by a sheath formed by upgrowth of the surrounding tissue 
Fig. 29. Vertical longitudinal section of female plant, traversing a receptacle. A. C. air- 
chambers ; P. pores ; Rhiz. rhizoids springing from the lower surface of the receptacle and passing 
down the groove in the stalk ; V. S. ventral scales ; Arch, archegonium. X 15. One of the * barrel- 
shaped ’ pores is shown above, in vertical section, x 120. 
Fig. 30. Vertical transverse section of female plant, traversing a receptacle. Lettering 
as in Fig. 29. X 1 5. 
