MARSILEACEAE. 1 1 



whorled, forming sheaths at the joints; fertile leaves 

 forming a short spike terminating the stem; epidermis 

 rough. 



Family 4. EQUISETACEAE. HORSETAIL FAMILY. 

 Branches when present, whorled; sporangia 1-celled, clus- 

 tered under the scales of the terminal cone-like spikes; spores of 

 but one kind furnished with narrow ribbon-like appendages 

 (elaters} attached at the middle, coiling around them when 

 moist and spreading in the form of a cross when dry and mature ; 

 epidermis impregnated with silica, rough. 



19. EQUISETUM. HORSETAIL. 



Perennial plants with extensively creeping rootstocks; stems 

 simple or with whorled branches, furrowed lengthwise, mostly 

 hollow; sporangia adhering on the under side of the shield-shaped 

 scales of the spike, 1-celled, opening down the inner side; spores 

 of one kind, with elaters. 



Stems annual; spikes not mucronate at summit. 



Stems of two kinds; the pale brown fertile ones appearing 



in spring before the green branched sterile ones. 

 Fertile stems branched and green when old, only the 



top withering. E. pratense. 



Fertile stems dying after fruiting. 



Sterile stems 6-19-furrowed, 30-60 cm. high. E. arvense. 

 Sterile stems 2O-4O-furrowed, 60-120 cm. high. E. telmateia. 

 Stems all similar, green, naked, branched, fruiting in 



summer. 



Sheaths closely appressed; branchlets not wing- 

 angled. E. fluviatile. 

 Sheaths loose, especially the upper one; branchlets 



wing-angled. E. Utorale. 



Stems perennial; spikes mucronate at summit, fruiting in 



summer. 

 Plant tall and stout; stems many-grooved. 



Branches numerous, regularly whorled. E. ramosissimum. 



Branches irregular, few or wanting. E. hyemale. 



Plants tufted, slender; stems 5-io-grooved. 



Sheaths 5-io-toothed; stems hollow. E. variegatum. 



Sheaths 3-toothed; stems solid. E. scirpoides. 



Equisetum pratense Ehrh. Stems annual, of two kinds, the fertile appear- 

 ing before the sterile, 15-30 cm. high; fertile stems at length green and 

 branched like the sterile ones; sterile stems with 8-20 ridges and furrows, the 

 slender branches in whorls, mostly 3-angled; sheaths cylindric or somewhat 

 broadened at top, those of the stem with 10-12 teeth, those of the branches 

 3-toothed. 



Vancouver Island, Macoun. 



Equisetum arvense L. Common Horsetail. Aerial stems annual, of two 

 kinds, the fertile pale-brown and short-lived, appearing in early spring before 



