KEY TO THE SPECIES OF EQUISETUM. 



SERIES I. Evergreen species. Stems rough, seldom branched, 

 catkins usually tipped with a hard 

 point 



Stems tall, stout, about as thick as a lead pencil 

 Sheaths dilated upward 



Margins incurved, stems rough 



E. Funstoni 



Margins not incurved, stems smooth 

 E. l&vigatum 

 Sheaths not dilated upward 



Old stems much branched E. robustum 

 Old stems seldom branched 



Joints short. . E. hicmale 



Joints longer . E. Ferrtssi 



Stems slender, tufted 



Six-angled-, thread-like E. sctrpoides 



More than six-angled, larger E. variegatnm 

 SERIES II. Deciduous species, Rootstock only, perennial. 

 Stems smooth, usually branching, catkin 



not tipped with a hard point 

 Fertile stems tawny or flesh-coloured when young 

 Not lasting through the summer 



Plants stout, Western . E. Telmatcia 

 Plants slender, mostly Eastern E. arvense 

 Lasting through the summer 



Branches of sterile stems unbranched 



E. pratcnse 



Branches of sterile stems again branched 

 E. sih'aticuin 

 Fertile stems green like the sterile 



Sheaths appressed . E. fluiriattle 



Sheaths looser 



Spores perfect, abundant E. palustrs 

 Spores imperfect, few /'. 



