64 BRITISH HEPATIC^. 



Fronds (f. 10, 1) either creeping loosely among the tufts of Frul- 

 lania, Radula, &c., or forming dense fasciculate patches of a dark 

 indigo-green colour. 



Stems about the thickness of horse-hair, of a purplish-black 

 colour when mature, paler when young, rigid, polished, flexuose, 

 brittle when dry, erect or reclinate. 



Rootlets tew, distant, white, confined to the creeping stems. 



Shoots (f. 10, 2) ^" to 1", rarely 2" in length, rigid, recurved -at 

 the apex, very slender, from ■^" to -^" in diameter, branches 

 alternate, divaricate, recurved at the apex, of nearly uniform size 

 throughout, sometimes attenuate. 



Leaves (f. 10, 3, 4) distant, alternate, distichous, sub-vertically 

 patent, obovate or cuneate, from a contracted scarcely decurrent 

 base ; dorsal margin entire, apex bi-dentate, the segments acute, 

 unequal and divergent, sinus acute but shallow, ventral margin 

 reflexed, either entire or unidentate near the summit. !From the 

 recurvation of the upper half of the leaf the foliage appears at 

 right angles with the stem, or squarrose ; the terminal leaves only 

 are erect. 



Texture firm, rigid, sub-opaque ; coTour dark olive or indigo- 

 green, appearing nearly black when dry. From the narrow inser- 

 tion of the leaves they are readily detached when dry, but less so 

 than in the following species. 



Amphigastria (f. 10, 8) generally present, minute, distant, 

 recurved, bi-dentate. 



Cells (f. 10, 3, 7) distinct without preparation, roundish, con- 

 taining numerous chlorophyll corpuscles, thickened somewhat at 

 the angles. 



Marginal cells ttt? " by two" 5 those of the upper third ■^" 

 to TTs" ; basal cells yJo" to tto" by tiW- 



Trigones -j-^go^" iii diameter. 



Androecitim spicate, ovate (f. 10, 2). 



Perigonial leaves (f. 10, 5) 3 to 6 pairs, larger than those of 

 the stem, closely imbricated, saccate at the base and concealing 

 the stem, ovate, multi-dentate. 



Antheridia 1 or 2, roundish, pale olive-yellow, shortly stipitate. 



Obs. — Plag. tridenticulata appears to have been looked upon by Hooker and Lin- 

 denberg as the male plant of P. spinulosa, until Dr. Taylor discovered the perigonial 

 shoots of the latter, and pointed out the differences between them. The species, 

 indeed, is a very distinct one, but hitherto only male and barren fronds have been 

 met with. 



Setting aside the much smaller size and distant cuneiform divergent leaves, the 

 shape of the androecium is very characteristic, forming in P. tridenticulata short tumid, 

 ovate spikes of few leaves, wider than the ordinary ones, and nearly always terminal ; 

 whilst in P. spinulosa the perigofiial leaves are more numerous, laterally compressed, 

 and forming a narrower lanceolate spike, beyond which the stem is often continued in 

 a proliferous manner. 



