110 BRITISH FERNS. 



been met with only in a limited number of localities in 

 Ireland, Scotland, and the north of England. 



THE CORN-FIELD HORSETAIL. 



This is the Equisdum arvense of botanists. It is the most 

 common of the species, and in many places is an injurious 

 weed, very difficult to eradicate. It occurs here and there, 

 almost everywhere, in fields and waste places, especially 

 where the soil is sandy. It has long, creeping, underground 

 stems, which are a good deal branched, and are cylindrical 

 and jointed in the same way as the stems which rise above- 

 ground. The stems which appear aboveground are of two 

 kinds, the one simple and fertile, the other branched and 

 barren. 



The fertile stems are quite without branches, and grow 

 up early in spring, in April and May, arriving at maturity and 

 perishing long before the barren ones have completed their 

 growth. They are from three to eight or ten inches in height, 

 hollow, succulent, and nearly smooth. The sheaths are 

 large and loose, widening upwards, pale-coloured, divided 

 into about ten dark-brown teeth, which often adhere together 

 in twos and threes. _ The teeth are very narrowly lance- 

 shaped and sharp-pointed, and correspond with the ribs, 

 about ten in number, by which the sheaths are marked. 

 These stems are terminated an inch or two above the upper 

 sheath, by cone-like heads, rather more than an inch long. 



The barren stems are either erect or decumbent, and from 

 one to two feet or more in height; they are generally 

 branched from bottom to top. They spring up after the 

 fertile stems have withered, and are at first crowded with 

 short appressed branches, which, by degrees, become elon- 

 gated, and spreading, and are sometimes again branched. 

 The main stem has from ten to sixteen distinct shallow 

 furrows, with corresponding ridges, and is, as well as the 

 branches, studded over with minute silicious warty particles. 

 The sheaths, which fit somewhat closely to the stem, are 

 furrowed like it, and terminate in an equal number of acute 

 wedge-shaped dark-coloured teeth, which are often margined 

 by a narrow brown membrane. The branches are four- 

 ribbed and four-angled, and their sheaths four-toothed, the 

 teeth being long and acute. 



The section of the stem of E. arvense shows an interior 

 cavity occupying only about one-third of the diameter. The 

 exterior surface is varied by about a dozen blunt ridges, hav" 

 ing corresponding shallow depressions ; within this, occupy- 



