THE SCOURING-RUSHES. 



of the most conspicuous differ- 

 ences among the equisetums 

 is found in the duration of 

 the aerial stems. In some 

 species all traces of them 

 above ground disappear soon 

 after the first hard frost, 

 while in others the stems not 

 only endure at least onewin- 

 CROSS-SECTION OF STEM. ter, but in the second season 



possess enough vitality to put forth new branches. 

 It is singular, also, that the evergreen species should 

 all resemble one another in external appearance more 

 than they do the species with deciduous stems. To 

 divide the genus upon the single character of perennial 

 or deciduous stems would separate the species into two 

 very natural groups. It has been proposed to make 

 these two groups separate genera, though botanists at 

 present usually include the two in the single genus 

 Eqiiiseturn ; the evergreen species, however, are placed 

 in the sub-genus Hippoc/uetCE. 



The Common Scouring-Rush. 



Undoubtedl}^ the best known of the evergreen equise- 

 tums is the common scouring-rush {Eqtiisetiim luemalc). 

 Its stiff unbranched stems of dark green, ringed at the 



