THE AMPHIBIOUS QUILLWORT. 239 



of Isoctcs Canadensis ; but it is probable that Isoctcs 

 riparia does not occur in New England. This is doubt- 

 less the plant that has so frequently been mistaken for 

 that species in this region. 



Isoctes Canadensis has been found in various localities 

 from Maine to Pennsylvania, and also in Ontario and 

 British Columbia. It is doubtless more abundant than 

 it is at present known to be. It' grows in shallow water 

 in rivers. 



T'he River-Bank ^illwort. 



The river-bank quillwort {Isoctcs riparia) was found near 

 Philadelphia by Nuttallin i8i5,but, as was usual in those 

 days, it was referred to the common European Isoetes 

 lacustris, and it was not until thirty years afterward that 

 its distinctness was recognised and the name it now 

 bears ^\'as assigned to it. 



Isoctcs 7-iparia is a medium-sized species with from 

 fifteen to thirty round leaves that oc- 

 casionally reach a length of a foot, but 

 are commonly several inches shorter. 

 The leaves have abundant stomata, are 

 without bast bundles, and the sporangia 

 are spotted and about one third indu- 



r^. ^ Megaspore of 



Slate, i he megaspores are 45O/" to 050/" isocus riparia. 

 in diameter, with thin, jagged, irregular crests that so 

 nearly resemble those of both Isoctes lacnstris and 

 Isoetes Tiickcrmani that good students of the genus can- 

 not always agree as to their identity. They maj/ usually 

 be distinguished from Isoetes Tuckerniani, however, by 

 the crests being more numerous, thicker, and longer, 

 and from Isoetes lacnstris by the crested commissures. 



