DESOEIPTION OF SPECIES— EQUISETACEiE. 67 



EQUISETACE^. 



EaUISETUM, Linn. 

 Eqnisetuin Haydn iiii, Lesqz. 



Plate VI, Figs. 2-4. 

 EquUetum Haydenii, Lesqx., Annual Report, 1871, p. 284 ; 1872, p. 385. 



Rhizomas thick, cylindrical, irregularly distinctly striate, articulate ; articulations distant, bear- 

 ing large oval or obovate tubercles narrowed to a round point of attachment, in whorls of eight to ten 

 around the articulations. 



The rhizomas, flattened by compression to about two centimetres in 

 width, are regularly cylindrical, slightly narrowed only at the articulations ; 

 these are distantly marked around by circular scars at the point of attach- 

 ment of oval or obovate tul)ercles, averaging two centimeters in length 

 and one and a half centimeters broad; the rhizomas are distinctly irregularly 

 striate, the tubercles ob.scu rely ribbed in the length, either simple and joined 

 to each other by their ends, like a string of beads, or double, two of them 

 being attached to the inflated end of a single one, as on the right side of fig. 3. 

 At a distance from the point of connection to the rhizomas, and as seen from 

 the numerous fragments of this species covering large slabs, the tubercles 

 become more and more elongated, and pass to mere cylindrical filaments, or 

 rootlets, which appear to divide into radicles. The point of union of the 

 tubercles, either to each other or to the rhizomas, is marked by comparatively 

 large scars, three to four millimeters wide, representing a double ring with 

 a central point. Fig. 4 represents one of these tubercles split lengthwise, 

 and exposing in the middle a central solid axis, one and a half millimeters 

 thick, while the parietes or intervals from the axis to the borders, four milli- 

 meters each side, appear formed of a spongy though compact medullar tissue, 

 becoming more compact or darker-colored near the borders. A vertical 

 cross-section of another tubercle from Carbon specimens, like the former, 

 shows it to be oval or somewhat flattened by compression, twelve millimeters 

 in one direction and only nine in the other. Still another sjiecimen of the 

 same locality represents a linear rootlet, or rhizoma, whose main axis, four 

 millimeters wide and central, appears surrounded by a cylinder of cellular 

 tissue of equal thickness. This branch is marked by distant nodi and round 

 scars, the same as those of Barrell's Springs, from which the species was first 

 described. This species is comparable to Equisetum arcticum, Heer (Spitz. 

 Flor., p. 31, pi. 1, figs. 1-15), which has narrower rhizomas, with nearly as 

 large tubercles, more elongated and narrower at their point of attachment, 

 and also to Physagenia (^Equisetum) Parlatorii, Ung. (Sillog., p. 4, plate 1, 



