PERNS OP GREAT BRITAIN. 145 



Order IV. EQUISETACE^.— HORSETAILS. 



1. Equisetum (Horsetail). 



1. E. arvense (Cornfield Horsetail). — Barren stems 

 with few furrows, slightly rough. ; branches rough, with 

 three or four simple angles ; fertile stem unbranched, 

 with few loose distant sheaths. This is by far the com- 

 monest of our native Horsetails, some of which are known 

 to all who observe the plants which grow wild. These 

 plants are commonly called Jointed Ferns, or Leafless 

 Eerns, though they have not a very obvious afiinity with 

 the leafy species commonly recognised as ferns. They 

 are destitute of any green expansions ; they are jointed 

 at regular intervals, the joints or knots being solid, and 

 surrounded by membranaceous toothed sheaths, while 

 the portions between the joints are hoUow. Their 

 branches are rigid and whorled, and the fructification 

 placed in cone-like heads made of scales, to the lower 

 face of which the seed-cases are attached in a row round 

 the margin. 



The stem is chiefly composed of cellular matter, but 

 towards the outer portion there is a layer of woody 

 fibre. The cuticle, or thin skin, which covers the Horse- 

 tails, is in all the species regularly and beautifully decked 

 with particles of flint, arranged in lines and other forms, 

 often not the five-hundredth part of an inch in diameter. 

 These particles were discovered by Dr. Brewster to lie, 

 in the greater number of cases, in simple straight lines ; 

 but others are grouped into oval forms lilce the beads of 



