EQUISETACE^E. 171 



lanceolate-subulate gradually-acuminate teeth, having rather narrow 

 scarious margins ; this form may be the var. pseudo-elongatum of 

 Milde. 



I have been unable to procure specimens of the Killarney plant, on 

 which the var. Wilsoni was originally founded. It seems to be a much 

 larger plant than the Dublin Canal one. Mr. Newman describes a 

 stem which he believes to be of average size, and says it is 38 inches 

 long, one-third of which was submerged, and from his figure of it, it 

 must have been as thick as a goose-quill. He considers the average 

 number of furrows as 10, " the ridges between them being broad, as in 

 the common form, but the silicious particles are far less prominent, so 

 that the plant does not partake of that asperity which so eminently 

 characterises E. hyemale, E. Mackaii, and the more usual forms of 

 E. variegatum, but has a smoother feel like that of E. palustre. . . . The 

 sheaths are scarcely larger than the stem, with which, in dried speci- 

 mens, they appear perfectly concolorous, with the exception of a 

 narrow sinuous black band at the summit of each." (Brit. Ferns, 

 ed. ii. pp. 39, 40.) Mr. Newman considered that the Mucruss plant 

 was not the same as that from the Dublin Canal and Kincardineshire. 



E. variegatum, or at least the stouter forms of it, is liable to be con- 

 founded with E. trachyodon, but the sheaths of the latter are cylin- 

 drical and closely applied to the stem, and they have long subulate, 

 rather rigid teeth. In E. variegatum the sheaths widen upwards, and 

 then contract ; the teeth are considerably shorter than in E. trachy- 

 odon, even in those cases in which they are gradually acuminated. 

 It is very rarely that the whole sheath becomes black, as they so 

 commonly do in E. trachyodon. 



Small forms of E. palustre have sometimes been mistaken for 

 E. variegatum, but that plant has the stem-ridges without a furrow 

 on their back, and without the two distinct rows of silicious tubercles 

 on the ridges, which like the spaces between them, are only trans- 

 versely rugose ; the furrows of the sheaths which correspond to the 

 divisions between the teeth are deeper, and the portion between these 

 furrows more convex and without a central furrow until near the 

 apex, while the lateral furrows, which are distinct in E. variegatum, 

 are wanting in E. palustre ; the teeth of the sheaths in E. variegatum 

 are usually much longer and sharper than in E. palustre, and the 

 spike of the latter is not apiculate or mucronate. 



The stems of E. variegatum are completely evergreen, and the 

 spikes more frequently survive the winter in this than in the other 

 Equiseta hyemalia, although it occasionally happens to them all ; 

 when it does so, the spike in spring becomes slightly exserted and 

 paler in colour. 



It seems probable that under the name E. hyemale, Linna3us 

 included not only the plant usually called E. hyemale by modern 

 botanists, but also all the forms of the Equiseta hyemalia (the 

 section Hippochsete, Milde). The same view was taken by Mr. 



