BRITISH HEPATIC^. 61 



composed of elongated thickened cells, in which the cavity is nearly- 

 obliterated. 



Shoots from one to four inches in length, by -^" to \" in dia- 

 meter (f. 14, 1, 2), clothed with rather distant or more closely 

 imbricated distichous alternate leaves : in some specimens the 

 leaves are so much decurved as to appear secund. Barren shoots 

 are of nearly equal width throughout, but the ultimate flagellse 

 are much more slender, and clothed with minute caducous leaves, 

 so that at certain times of the year they appear almost as bare as 

 the stolons. 



Leaves (in the larger English form (f. 14, 1, 3, 8)) from ^j" 

 to ■^" in length, broadly-ovate, deltoid-ovate or obovate, rather 

 distant, semi-vertically patent, insertion broad oblique, dorsal 

 margin entire, decurrent for some distance, reflexed, apex obtusely 

 pointed, 2-3-dentate, ventral margin irregularly dentate, strongly 

 recurved. 



In 3 pimctata (f. 14, 2) the leaves are more variable in size and 

 shape, those of the main shoots (f. 14, 5) broadly-ovate, very convex, 

 boldly decurrent, patent-divergent, or sub-secund, and fringed with 

 closer and more rigid spinose teeth. 



On the ultimate flagellse the leaves are not much broader than 

 the stem, sub-vertically patent, cuneiform, 2^3-dentate, the base 

 narrow and scarcely decurrent. 



In S inermis the leaves are roundish- ovate, truncate or un- 

 equally bidentate, with short segments and obtuse sinus, margins 

 reflexed, and for the most part entire, although, on careful ex- 

 amination, one or two irregular teeth may generally be found at 

 the base of the older ones, 



Amphigastria usually present, but distant and irregular, except 

 on the innovations, minute, deeply 2-3-fid. 



Texture firm, little altered when dry, in a pale yellowish-green, 

 sub-pellucid, in 3 more rigid, of a warmer olive-brown tint, and 

 punctate-reticulose. 



Areoldtion " dotted or guttate " (f. 14, 1, 5), trigones large, 

 conspicuous, so that under a low power the true cells appear to be 

 surrounded by a border of smaller ones, and the leaf must be pre- 

 pared before the true outlines are developed. 



Marginal cells smaller, sub-quadrate, ste" by tiW; ii the 

 lower part of the leaf (f. 14, 11) hexagonal, ■^" to 4^" by 



Those of the spines are from yoo" to T¥oo" lo^ig by xi^" to 

 t-JLq" broad. Trigones about -rho" ii diameter. 



The cells of Tlag. spinulosa differ in no respect from those of 

 P. pwnctata, Tayl., except that the latter are filled with a more 

 abundant golden-brown chlorophyll, so that the interior is mor6 

 distinctly defined, and the leaf appears ' dotted.' 



This kind of tissue, ' textura porosa,' resembles under the mi- 



