252 THE TERRESTRIAL QUILLWORTS. 



leaf bases and a broader indusium is called the variety 

 pallida. 



Isoetes Butleri. 



Closely related to Isoetes mclanopoda by spore charac- 

 ters, at least, is the species called Isoetes Butleri, which 

 is able to grow in even drier localities, and closely 

 approaches our idea of a terrestrial species. The effect 

 of the lack of moisture is doubtless shown by the fact 

 that it is a smaller plant with shorter and fewer leaves. 

 It shows its dependence upon water, however, by 

 disappearing earlier in the year than Isoetes melanopoda, 

 often, in the South, before the first of July. 



In this species the sexes seem always to be separate. 

 The megaspores are larger than those 

 of Isoetes vielanopoda, measuring from 

 400 /" to 600 P in diameter, and marked 

 with heavier warts or points; otherwise 

 they are quite like them. Isoetes But- 

 ler i has been reported from Missouri, 

 Megasporeof Oklahoma, and Tennessee, and is as 



Isoetes Butleri. 



yet a rare species. It doubtless occurs 

 at many 'other points. The variety iinmaculata is larger, 

 with unspotted sporangia. 



Isoetes Nuttallii. 



Isoetes Nuttallii is a species of the Northwest, first 

 found along the Columbia River, in Oregon, by the 

 botanist whose name it bears. It is usually about three 

 inches in height, with firm, erect leaves from twenty to 

 sixty in number. It grows in wet places, but apparently 

 never under water. The sporangia are entirely covered 

 by the indusium, and the megaspores are usually quite 



