THE SCOURING-RUSHES. 21 



winter-killed long before such a condition is reached. 

 Mature stems seldom reach a height of more than four 

 feet, or a diameter at base of half an inch. 



A series of joints in the stem divide it into many sec- 

 tions, each three or four inches long. At the top of each 

 section, or internode, there is a leaf-sheath a quarter of 

 an inch or more long, fitting closely around the base of 

 the next internode, and bearing on its summit numer- 

 ous small triangular teeth which end in a long point. 

 These teeth are jointed to the sheath and usually fall 

 away at maturity, being noticeable only in very young 

 stems. Often the tips coalesce in the bud, and, as the 

 stem lengthens, they are carried upward on its summit 

 in a compact mass resembling an old-fashioned candle- 

 extinguisher or a Chinese pagoda. 



Where the sheath joins the stem, there is a brown or 

 blackish band, and a line of the same colour borders the 

 outer edge. Between these the colour is purplish, green- 

 ish, or ashy white. The width of the black band and the 

 colour between them varies with age and with the indi- 

 vidual. In some specimens the bands always remain nar- 

 row, while in others they may broaden until the entire 

 sheath is suffused with black. This latter is most, com- 

 mon in old stems and in sheaths near the base. The 

 marginal band is always the darker of the two, and in 

 young specimens the second band is frequently missing, 

 or is indicated only by a faint brown line. No species 

 show the manner of jointing better than this. After the 

 stem has been pulled apart it may be easily reconstructed 

 on account of the nicety with which the ends of the 

 internodes fit into the sheaths. At the nodes or joints 

 the stem is solid, but cross-sections, of the internodes 

 show a very large central cavity occupying four fifths of 



