224 THE AQUATIC QUILLWORTS. 



The Lake 



The lake quilhvort (Isoetes lacustris) was not named 

 because it is the typical quilhvort of our lakes, but be- 

 cause it was first found and is quite abundant in the lakes 

 of Europe. There are good botanists 

 who doubt that it has ever been found 

 in America, though it was often re- 

 ported by early collectors. At that 

 time, however, it was customary to 

 refer all our plants to Old World species 

 of similar appearance, and this probably 



Isoetes lacustris, i . i r -. 



explains the many reports of its occur- 

 rence in regions where nowadays it cannot be found. 



Isoctcs lacustris is described as having from ten to 

 thirty dark-green leaves from three to six inches long. 

 There are no stomata in the leaves, and the indusium cov- 

 ers about one third of the unspotted sporangium. The 

 megaspores are from 500^ to Soo /" in diameter, marked 

 all over with short, thin, wavy ridges. The microspores 

 are 35 /" to 45 /" long, light grey, and smooth. The Ameri- 

 can plant differs from the European in the larger mega- 

 spores, and Durieu proposed that it be called Isoctcs 

 macrospora. It would seem wise, in view of the appar- 

 ent absence of true Isoetes lacustris, to refer all our plants 

 to Isoetes macrospora. Mr. A. A. Eaton concurs in this 

 opinion, but since Isoetes lacustris has long had a place in 

 our flora we have here included Isoetes macrospora with it. 



The typical Isoetes lacustris is spread widely through 

 the lakes of northern Europe, and is well enough known 

 to receive the common name of " Merlin's grass." It 

 grows in from one to six feet of water. Fish are said 

 to be fond of the tender leaves, and are reported some- 



