19 17- Praeger — Equisetum litorale in Ireland. 143 



regards the forms of the plants prevailing locally. — was 

 collected, from which the following notes were compiled : 



E. arvense — barren stems (which alone remained) 6-12 

 inches long, seldom erect, but usually ascending and 

 branched from the base, with the branches longest below, 

 giving a triangular or ovate outline ; when growing strongly 

 among vegetation, the stems attained 18 inches in height, 

 and were then bare in the lower half, the outhne of the 

 upper half tending to oblanceolate, with a short abrupt 

 tail. Stem (middle part) about 8 mm. in circumference, 

 strongly furrowed, very firm if compressed laterally, feeling 

 almost solid. Teeth 7 or 8 in number,^ long-triangular, 

 2.5 — 4 mm. long. In cross section the central hollow occupies 

 about J of the diameter, the lacunae in the walls (7-8 in 

 number) being small in comparison, and oval with the 

 longer axis radial (not almost as large as the central hollow 

 as in E. palustre). Layer of thickened cells just inside the 

 ring of lacunae well-developed, causing the stem if crushed 

 to separate readily into an inner and outer C3dinder. 



E. limosum — as developed locally varies much in length 

 and thickness of stem, and is branched or unbranched ; 

 stems usually 2-3 feet long, quite erect, dark green, bare 

 in lower half or more, branched portion lanceolate in outline, 

 ending in a long naked tail ; cone black and thick. Stem 

 about 12 mm. in circumference, almost smooth, with many 

 faint furrows, weak, collapsing on slight lateral pressure. 

 Teeth about 15, crowded, very narrow, 2 — 2.5 mm. long. 

 Central hollow occupying about J of the diameter ; the 

 lacunae (about 15) in the thin wall very small or absent, 

 oblong with long axis parallel to the circumference. No 

 layer of thickened cells, to cause the stem to divide, if torn, 

 into an inner and outer cylinder. 



E. arvense x limosum? — Erect, usually about 2 feet high, 

 fresh green in colour, bare in lower half or more, branched 

 above, the branched parts lanceolate in outline with a 



1 In the Horsetails, the number of teeth (the tips of the rudimentary 

 leaves), of ridges (when the stem is rough), of air-spaces in the cortex 

 (the '* vallecular lacunae "), &c., depends upon and equals the number 

 of the fibro-vascular bundles. This number is quite variable in most of 

 the species. In E. arvense it ranges from 6 to 19 (being usually from 

 8 to 12) ; in limosum from 10 to 30 (usually 16 to 20). 



