THE AMPHIBIOUS QUILLWORT. 239 



of Isoctes 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. 



The River-Bank O^uillwort. 



The river-bank quillwort (Isoctes riparid) was found near 

 Philadelphia by Nuttallin 1815, but, as was usual in those 

 days, it was referred to the common European Isoetcs 

 lacustris, and it was not until thirty years afterward that 

 its distinctness was recognised and the name it now 

 bears was assigned to it. 



Isoetcs riparia 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- 



. , .-pi x- Meg-aspore of 



siate. The megaspores are 450^ to 650 /" hoefes nfaria. 

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

 nearly resemble those of both Isoetcs lacustris and 

 Isoetes Tuckermani that good students of the genus can- 

 not always agree as to their identity. They may usually 

 be distinguished from Isoctes Tuckermani, however, by 

 the crests being more numerous, thicker, and longer, 

 and from Isoetes lacustris by the crested commissures. 



