THE AMPHIBIOUS QUILLWORTS. 237 



megaspores, curiously enough, are smaller than the aver- 

 age, being from 300/^ to450'Mn diameter. The mega- 

 spores of Isoctes Eatoni are described as being marked 

 with "convolute labyrinthiform ridges, cristate on the 

 angles of the inner face." The markings of the spores 

 alone are nearly sufficient to constitute this a good 

 species. They appear like those of Isoctes Engclmanni, 

 in which many of the connecting crests have disappeared. 

 The fact that the so-called variety valida is described as 

 having spores smaller than the type is also significant. 

 Mr. Eaton, who has made a very careful study of this 

 genus, is of the opinion, however, that the two forms are 

 not identical. 



If we consider them two forms of one species the 

 range may be given as from New Hampshire to Dela- 

 ware and Virginia. The plant is rare, however, and has 

 been found only in a few localities within this territory. 

 A curious thing about the plants from New England is 

 that they appear to be dicecious. Microspores are seldom 

 found, but the megaspores are abundant. It is surmised 

 that the same sporangium may occasionally bear both 

 kinds of spores, as is sometimes the case in Isoetes Titck- 

 erviani. 



Isoetes Canadensis. 



The history of the quilhvort now called Isoetes Cana- 

 densis is a good illustration of the way small and easily 

 overlooked differences may affect our conception of 

 species in the genus Isoetes. It was first called the variety 

 Canadensis of Isoetes riparia. Later the same species was 

 found in New England, and, its identity being overlooked, 

 it was described as Isoctes Dodirei. The name first given 



