64 THE HORSETAILS. 



the long basal branches, or a few of those near the tip, 

 may bear small cones of fruit also. 



The sheaths in both fertile and sterile fronds are 

 longer than broad, greenish in colour, with rather loose 

 black teeth bordered with white margins. They invest 

 the stem quite loosely, being dilated upward. The 

 leaves are convex, grooved in the middle at the apex, 

 and strongly keeled below. 



The stems have from five to twelve broad, deep 

 grooves, the ridges separating them being narrower, 

 sharply elevated, and rounded on the back. These 

 grooves are fewer in number than in tLquisetum fluviatile 

 and in fresh specimens are much more prominent. 

 When dried for the herbarium the difference is not so 

 marked. The branches usually contain fewer angles 

 than the stem, and their sheaths are also green and 

 dilated. The central cavity of the stem occupies about 

 one sixth of the diameter, a character which alone is 

 sufficient to distinguish it from Eqiiisetiun fiuviatile. 

 Carinal and vallecular canals are also present. Although 

 so much like the water horsetail, it occasionally pro- 

 duces forms that are very much like varieties of 

 Eqiiisetnin arvensc, and the likeness is heightened by 

 the similarity of the internal structure of the stem. 



The marsh horsetail has been reported from all the 

 New England States except Rhode Island, and from 

 Illinois and Washington. In none of these States is 

 it abundant or extensively distributed, and in many 

 the record rests upon a single locality. It is more 

 plentiful in British America, extending to Alaska and 

 Hudson Bay. It grows among grasses in damp mead, 

 ows, in moist woodlands, and in open swamps. Dr. C. 

 B. Graves has found it in Connecticut in meadows sub- 



