THE EQUISETACE/E. 



OT inappropriately may the Scour- 

 ing-Rushes be likened to the 

 cacti, for, like them, their leaves 

 are reduced to mere rudiments, 

 and the stems perform all the 

 offices usual to leaves. This, 

 however, is not their only 

 peculiarity. In their general 

 structure they have little re- 

 semblance to other plants. The stems are jointed, hollow 

 except at the joints, and noticeable for their lack of 

 differentiation from the underground portion of the 

 plant. From the farthest subterranean root-stock to the 

 tip of the tallest shoot, the construction is essentially 

 the same. It may be likened to a line of drain-pipe, each 

 section of which fits into the slightly flaring top of the 

 one below it. These hollow sections are grooved exte- 

 riorly with from three to fifty longitudinal grooves, vary- 

 ing in number with the species. These grooves are 

 known as valleculae and the intervening ridges as carinae. 

 Within the stem walls, and encircling the central hollow, 

 there are "usually found two other series of hollows, 

 one series beneath the valleculae, and therefore called the 

 vallecular canals ; the other beneath the carinae, and called 



