30 THE SCOCRINORUSHES. 



the stem, and by the appressed sheaths and strongly 



apiculate catkin. 



It is not known at present whether this form occurs 



elsewhere, or whether its existence at Joliet is unique. 



At the place where it was discovered it forms an exten- 



sive thicket, but this may have arisen by means of the 

 spreading rootstock. Possibly the first plant was 

 produced by a variant spore. If so, it is not 

 likely to be found in other localities, and the 

 question arises whether it is entitled to be called 

 a species, or is more properly considered a form 

 of Eqnisctum Jiicmalc. From the modern view- 

 point of evolution it might be thought an off- 

 shoot, by mutation, of the species mentioned. 

 In form it appears to be more distinct than either 

 Equisetum hiemale robustum or Equisetum hiemalc 

 medium; but should it turn out to be un- 



^ D ' worthy of specific rank it would still rank as a 

 sub-species with the title of Equisetum hiemale Ferrissi. 



The Smooth Scouring- Rush. 



Typical specimens of the equisetums are not difficult 

 to identify, but when one has a large series of a single 

 species from different localities to deal with, the task 

 becomes more perplexing than might be supposed, on 

 account of the numerous variations presented ; in fact, 

 it is hinted that all the species in the section Hippochcetc, 

 though distinct enough as to type, may be connected by 

 intergrading forms. One of the most variable of these 

 species is the smooth scouring-rush (Eqnisctum hcviga- 

 tum). On the one hand it is linked to the common 

 scouring-rush by the form known as Eqnisctum hicuialt 



