691 



pasture land in the Isle of Dogs, I observed that nearly every stem 

 within reach from the bank had been cropped at a nearly uniform 

 height : horses, horned cattle and sheep, are constantly feeding in 

 these meadows. 



The roots of the water Equisetum are numerous, black, fibrous and 

 sinuous : they spring from the bases of the submerged sheaths in a 

 manner precisely similar to that of the branches, and those which ori- 

 ginate near the surface of the water not unfrequently ascend for a 

 time in the same way. The rhizoma is creeping, and extends hori- 

 zontally in every dii*ection, forming a matted mass in the mud of 

 ponds and ditches where the plant occurs : it is of a brown colour, 

 with jet black sheaths, which are rather more approximate than in 

 ascending stems, but in other respects scarcely different. In winter, 

 when the exposed portion of the stem of the preceding year is dead, 

 the remaining portion becomes prostrate on the mud, still however 

 retaining some of those lower branches which may be seen in the sum- 

 mer in a state of incipient development : these, together with others 

 in a still younger state, fonn the ascending stems of the ensuing year. 



The engraving at page 689 represents a moderately sized stem of 

 the water Equisetum, of its natural size and proportions : a much 

 larger might have been selected, but its representation would have 

 been more difficult. The stem is perfectly erect, and about twenty- 

 five inches in height, of which seventeen inches were above water and 

 the remainder submerged. The submerged portion is smooth, the 

 apical portion slightly striated (the striae are much more distinct in 

 immature and barren stems) ; its average diameter is a quarter of an 

 inch : it is divided by transverse septa into thirty compartments, thir- 

 teen of which were above, and the remainder below the surface of the 

 water : the internodes above water vary from three quarters of an inch 

 to an inch and three quarters in length ; those submerged are very ob- 

 viously shorter. The sheaths are about a quarter of an inch in length ; 

 they are green, concolorous with the stem, and of nearly equal diame- 

 ter, so that they clasp it very tightly : the teeth are sixteen to twenty 

 in number, sharp-pointed, always distinctly separated, black or dark 

 brown, and not unfrequently furnished with a very slender white mem- 

 branous edge. There are six whorls of ascending branches : these 

 rise from the base of the sheaths from the second to the seventh in- 

 ternode inclusive. The branches in each whorl vary from five to 

 seventeen in number : they are divided into joints, varying from five 

 to ten in number, and have from five to eight striae with correspond- 

 ing ridges, which terminate in sheaths having the same number of 



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