PILULARIA. 211 



deepest interest to those who are truly observers of nature. 

 The merit of the adaptation is entirely due to Mr. Waring- 

 ton, of the Apothecaries' Hall. 



Genus XXI. PILULABIA, Linnaus. 



OF this genus, there is one British species, Pilularia globu- 

 lifera, the Pillwort, or Pepper-grass, a creeping-stemmed 

 species, with filiform grass-like leaves, growing in clusters 

 at intervals along the thread-like stems, and bearing the 

 almost sessile fructification at their base. The parts of 

 fructification differ considerably in position from those of 

 the allied genus Isoetes, in which the spore-cases are en- 

 veloped in the thickened bases of the leaves, those of the 

 Pilularia being quite free, and attached directly to the 

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

 They also differ in structure, the fructification of Isoetes con- 

 sisting of two different kinds of bodies, namely granular and 

 pulverulent bodies, occupying separate spore-cases ; while in 

 Pilularia the two kinds are produced within each spore-case, 

 the larger bodies occupying the lower, and the smaller ones 

 the upper parts. 



