i2 THE EQUISETACE^E. 



the carinal canals. These differ in size and shape with 

 the species, and thus form excellent characters for their 

 identification. 



At the top of each joint in the stem there is a 

 papery sheath which seems to form a socket 

 into which the next joint above it fits. This 

 sheath is toothed on its upper border, usually 

 with as many teeth as there are ridges in the 

 stem. From various indications it is evident 

 that this sheath represents a circle of confluent 

 but reduced and functionally useless leaves. 

 Inside the sheath (that is, in the axils of the 

 leaves) buds are formed, a bud for each leaf, - 

 and if these develop into branches they break 

 out through the base of the sheath in regular 

 whorls. In many species these buds always 

 remain dormant unless the tip of the stem is Section of 



. , Stem at 



injured, when a few near the tip may give rise the Sheath. 

 to short branches. 



Externally the stems are often coated with particles 

 of silex in many curious patterns, such as rings, bands, 

 granules, teeth, and rosettes; and, not infrequently, 

 abundant silex particles may be found lining the central 

 hollow. This silicious coating gives a characteristic 

 harshness to the stems of certain species, rendering 

 them useful for polishing woodwork and other articles. 

 The silex is usually most abundant on the carinje, while 

 the stomata the minute openings for transpiration 

 are distributed along the valleculae. 



The rhizome or underground portion of the plant is 

 often of considerable length, and spreads about in the 

 earth from a few inches to several feet beneath the Sur- 

 face. The sheaths at the joints also contain buds, and 



