EQUISETUM ARVENSE. 121 



kin, the genus Equisetum with about twenty-five living 

 species. The species of to-day are more simple in struc- 

 ture than some of those of geological ages. The order 

 is in its old age and has almost disappeared. 1 



1 Read on Fossil Equisetums in Seward's "Fossil Plants" or other 

 text-books that describe them. 



