THE FERN BULLETIN 



VOL. VI. JULY, 1898. NO. 3. 



THE GENUS EQUISETUM, WITH REFERENCE TO THE 

 NORTH AMERICAN SPECIES. 



By Alvah A. Eaton. 



FIRST PAPER. 



WHILE classed among the fern allies, the genus Equisetum 

 is essentially an isolated group, resembling the other or- 

 ders only in reproduction from spores, which produce 

 prothallia, with antheridia and archegonia. In company with 

 other Pteridophytes, it has a vascular system (/. <?., the cells are of 

 various forms and arranged in vessels, bast, epidermis, etc.), 

 through which they obtain the name Vascular Cryptogams, to 

 distinguish them from mosses, etc. (the Cellular Cryptogams), 

 whose cells are not so differentiated. 



Aside from these similarities, few affinities can be found, and 

 the place of the genus has long been a matter of opinion. It 

 seems to be related to the pines as well as to the ferns ; and the 

 calamites, so numerous in the Coal Measures of the Carboniferous 

 age, may be regarded as the common ancestor of Equisetaceae 

 and Gymnospermse. 



DISTRIBUTION IN" TIME. 



Few orders can boast of being older than Equisetum, though 

 Lycopodium was declining when the scouring-rushes were young. 

 It made its advent in the Triassic ; and some of the fossil forms 

 closely resemble some existing species. 



NUMBER OF SPECIES. 



Milde, in his Monograph, describes twenty-five species. These 

 Baker (" Fern Allies") cuts down to twenty. Whether this be on 

 account of superficial work, apparent in the volume in general, or 

 whether the species done away with are really not valid, can only 

 be determined by access to European herbaria. Several species 



