6o THE HORSETAILS. 



whorls of simple branches which grow successively shorter 

 upward, ceasing entirely six inches or a foot below the 

 apex, which thus extends above the bushy portion as a 

 slender whip-like prolongation. The lowest branches 

 are often a foot or more in length and seem more-in the 

 nature of secondary stems. Usually the branches are 

 much shorter and are disposed in regular horizontal 

 whorls, though often, especially toward the apex of the 

 stem, the symmetry of the whorls is destroyed by the 

 failure of certain branches to develop. It is not uncom- 

 mon, also, for both fertile and sterile stems to be entirely 

 without branches, in which event they might be mis- 

 taken for forms of the common scouring-rush. In 

 branched forms the lowest branches may occasionally 

 put forth a few branchlets, but usually the branches are 

 simple. 



The stems of this species are smooth and contain from 

 ten to thirty shallow grooves which are not very promi- 

 nent in the living plant, but become more marked in the 

 dried specimens. The sheaths are like the stem in 

 colour, about as broad as long, and closely appressed to 

 it. The teeth, separated from one another by rounded 

 sinuses, are short, sharp, and nearly black in colour. 

 According to A. A. Eaton, the number of grooves in the 

 stem and the number of leaves in the sheath increase 

 upward, so that the upper joints often contain a third 

 more than those below. The stem is hollow for about 

 four fifths of its diameter, none of our other species 

 equalling it in this respect. The carinal canals are 

 apparently always present, but the vallecular are often 

 wanting in growing stems, though very prominent in 

 older ones. The rootstock, which is about as thick as 

 the stem, is also hollow. It is usually not very deep in 



