PTEUIDOPHYTA. 



225 



Sub-Class 2. Heterosporous Equisetinae. 



The two orders which come under this head are united by the charcteristics, 

 that the verticillate leaves are not united into sheaths (Fig. 226), and that be- 

 tween each whorl of fertile leaves there is also a whorl of barren ones. The 



FIG. 226. A. fragment of Annularia. 



fertile whorls in ANNULARIES are situated about midway between the barren ones 

 (Fig. 227), but in ASTEROPHYLLITE.E they occur immediately above a barren 

 whorl (Fig. 228) and contain only half as many members as the latter. The 

 lower whorls bear macrosporangia with one macrospore, the upper, micro- 

 sporangia with many microspores. 



FIG. 227. Fragment of Annularia longi- 

 folia, with sporangia ; the leaves have 

 partly fallen off : a barren whorls ; s fer- 

 tile whorls. 



FIG. 228. Fragment of cone of Astcro- 

 pltyllites (Volltmannia elongata) : a and s 

 as in Fig. 227. 



The ANNULABI.E were distichous (Fig. 226), and presumably floating plants. 

 The ASTEKOPHYLLITE.E had verticellate branches. These also died out after the 

 Carboniferous period, at the close of the Paheozoio. 



W. B. 



