THE AQUATIC QUILLWORTS. 221 



The typical Isoctcs echinospora is an Old World species 

 found in the lakes of northern and central Europe. It 

 differs from our plant in having an unspotted sporangium, 

 a narrower indusium, and no stomata. These differences 

 have been considered sufficient to make our plant a sepa- 

 rate variety. There can scarcely be a doubt that the two 

 forms have arisen from a common ancestor. Our plant 

 holds the same position in North America that the type 

 does in Europe. In the "Ferns and Fern Allies of New 

 England," Dodge gives its habitat as " margins of ponds 

 often wholly submerged ; also on the muddy shores of 

 streams or on the tidal tracts of rivers, often where the 

 water is very brackish." The author has seen it in many 

 of the small glacial lakes of northern Pennsylvania, but he 

 has never collected it in a locality in which it was ever 

 likely to be above water. There seems, therefore, to be 

 some difference in its habitat in different parts of its range. 

 The fact that it bears stomata may be taken as an indica- 

 tion that it is prepared for an occasional exposure to the 

 air. 



Our plant ranges from Pennsylvania, Utah, and Wash- 

 ington to Alaska and Greenland. Ac- 

 cording to Baker it is also found in 

 Iceland. The American plant has 

 several forms or varieties. A stouter 

 plant with more numerous leaves and 

 abundant stomata is called the variety 

 robusta, and a form with long slender 



i ,1 ' 11 i ,1 Megaspore of 



spinules on the megaspores is called the isoetes echinospora 

 variety Boottii. Robusta is recorded as 

 growing in Vermont and New Hampshire, and Boottii 

 has never been found except in the few localities in 

 Massachusetts where Boott first found it. These forms 



