PILULARIA. 239 



and stocked with miniature fish, is an object of intense 

 interest. 



Genus XXIII. PILULARIA, or PILLWOHT. 



The Filula7'ia glohullfera, Pillwort, or Pepper-grass, is 

 a creeping-stemmed species, having filiform grass-like 

 leaves, which grow in clusters at intervals along the thread- 

 like stems, and bear the almost sessile fructification at 

 their base. The parts of fructification differ considerably 

 in position from those of Isoetes, in which the spore- cases 

 are within the thickened bases of the leaves, while those of 

 the Pilularia are quite free, and attached directly to the 

 stem, though seated at the base of a small tuft of leaves ; 

 they also differ in structure, that of Isoetes consisting of 

 granular and pulverulent spores, occupying separate spore- 

 cases, while in that of Pilularia the two kinds of sjiores 

 are produced within each spore-case, the larger bodies 

 occupying principally the lower, and the smaller ones the 

 upper parts. 



The name comes from pilula^ a little ball or pill, the 

 spore-cases having a nearly globular form. 



