XXIII] ANATOMY i8i 



lateral offshoot of the leaf, in fact a pinna. As it is a complex body, and 

 difficult to understand, the simpler type seen in Pilularia will be described 

 first (Fig. 463). The sporocarp is here spherical: cut transversely four 











-^'" x-»- '' 





Fig. 463. Pilularia globidifera L. A, transverse section of the ripe but still closed sporocarp, about 

 half-way up, at the limit between mega- and microsporangia. B, approximately median longi- 

 tudinal section of the same. (Both x 20.) The firm and resistant outer wall is formed of prismatic 

 cells, and has a hairy covering. It is lined, and the cavity partitioned by mucilaginous tissue styled 

 the "indusium," which swells with water when ripe and evacuates the sporangia : these are pro- 

 duced in four sori, attached to marginal receptacles. (From Luerssen in Rah. Krypt. Flora, Vol. in.) 



loculi are seen, containing numerous sporangia borne on four peripheral 

 receptacles, the whole being enclosed by a firm rind (Fig. 463, A). The 

 sporangia are of two sorts: megasporangia, each containing one megaspore 

 visible with the naked eye; and microsporangia each containing many 

 minute microspores. Cut longitudinally {B) the loculi are seen to extend 

 from base to apex of the sporocarp, the elongated receptacle usually bearing 

 microsporangia distally and megasporangia towards the base. Each loculus 

 is enclosed peripherally by part of the massive wall of the sporocarp, while 

 centrally it is enveloped by a mantle of soft tissue often called the " indusium." 

 The internal tissues become mucilaginous when ripe, and are liable to 

 swell on access of water. The external wall is composed of an outer 

 epidermis, with hairs and stomata, lined by two deep bands of hard prismatic 

 cells. Internally to this shell is softer parenchyma enclosing the vascular 

 strands, one of which supplies each receptacle, while two others run longi- 

 tudinally in each of the spaces between (Fig. 463, A). When the inner 

 tissues swell on access of water the shell breaks into quarters by longitudinal 

 slits, and the sporangia and spores are evacuated in a mass of mucilage. 



