2IO THE ISOETACE/E. 



species Isoetes lacustris. Although numerous species are 

 now known to occur in the waters of the Eastern States, 

 the early volumes on the flora of the region make no 

 mention of them. Scarcely fifty years have passed 

 since botanists began to study these plants understand- 

 ingly, and students are yet by no means agreed as to the 

 limits which should separate various species or the posi- 

 tion they should occupy as a group in botanical classi- 

 fication. Baker, in his " Fern Allies," places them in 

 the Selaginellacete ; Campbell, in " Mosses and Ferns," 

 considers them closely related to such ferns as the 

 adder's-tongue {Ophioglossiim) and the moonwort [Botry- 

 cliiuni) ; while still others believe that their structure 

 indicates a closer connection with the pines and their 

 relatives. They are nowadays usually placed in a sepa- 

 rate order, family, and genus, as we have placed them 

 in this volume. 



Notwithstanding the close superficial resemblance be- 

 tween the quilhvorts and other water vegetation, the 

 difference between them is quickly recognised as soon as 

 one has become acquainted with a single species. A 

 quiUwort is essentially a rosette of short, hollow, cylin- 

 drical, pointed leaves with sporangia in their axils. The 

 central axis to which these leaves are attached is short 

 and flat, so that there is never produced an elongated 

 stem, as in the other fern allies. If one can imagine a 

 fruit-spike of Selaginella in which the axis has failed to 

 develop, and in which the sporophylls have lengthened 

 into quill-like though flaccid leaves, he will have a good 

 idea of the typical quiUwort. The resemblance of the 

 plant body to the bulbs of flowering-plants has also been 

 frequently noted. 



The trunk, main axis, or rootstock, though flat and 



