48 HISTORY OF BRITISH FERNS. 



20. Tsoetes = Stemless, quill-leaved, aquatic plants, 



with the fructifications at the base, enclosed within 

 the bases of the leaves. 



21. Pilularia = Creeping, slender -leaved, aquatic 

 plants, with the fructification in globular, sessile, 

 four-celled spore-cases. 



IY. HOESETAILS EQUISETACE^. 



Elowerless plants, with peltate spore-cases, arranged in 

 terminal cones. This group consists of the genus 

 Equisetum. 



22. Equisetum = Jointed, tubular-stemmed .plants, with 



terminal cones of fructification. 



