THE AMPHIBIOUS QUILLWORTS. :245 



surface, though the wliole plant may sometimes be found 

 exposed. The sporangia are rather small and are com- 

 pletely covered by the indusium. The megaspores are 

 from 300 Z' to 400 /" in diameter and are marked in a dis- 

 tinct and reinarkable way. In some there is a single 

 large button-like tubercle in the centre of each of the 

 three areas outlined by the commissures and equator; in 

 others, there are several smaller tubercles in these areas. 

 On the lower hemisphere these tubercles incline to run 

 together, forming thick wrinkles. The equator and the 

 commissures are unusually heavy. 



Two, varieties of this species have been named. The 

 variety rigida is smaller, slenderer, with more erect leaves. 

 The variet}' Chapviani is distinguished by having larger 

 megaspores that are almost smooth on the upper hemi- 

 sphere. Thus far Isoctcs flaccida has been found only 

 in Florida. It may possibly occur in the southern parts 

 of the other Gulf States, but will probably always be a 

 rare species. 



Isoetes Howelli. 



Tills species may be described by saying that it is like 

 Isoetes Xuttallii, with the exception that the megaspores 

 are not so conspicuously marked with roundish warts, 

 but usually ha\e low crests that may be cither isolated 

 or confluent, especially in the lower hemisphere. The 

 spores are practically of the same size, often dark gre\' or 

 nearly black, and the author is inclined to regard it as a 

 form of Isoetes Nuttallii in spite of the differences in 

 habitat. 



The species has a larger number of leaves than Isoetes 

 Nuttallii, which is to be expected from its location under 



