sides. Antiieridia large, solitary in the axils of the perigonial
bracts.
Dimen.sions.— Stems l |- to 3 inches long, ’4 mm. diameter,
with leaves S' inm, wide; leaves, antical lobe 2' mm. x 1'75 nim.,
postical '8 mm. X'G mm., antical 2'1 mm. x '7 mm., postical
'75 min. x '5 mm. ; cells '0325 mm. x '0275 mm., '03 mm. x
'025 mm., '03 mm. x 0275 nun., '03 mm. x '03 mm.; '025 inm. x
025 mm.; stijmles 1' mm. x '75 mm., 1' mm. x '85 mm.; sub-bract,
antical lobe i '25 ram. x '55 mm., postical '75 mm. x '35 mm.; bracts,
antical lobe I'G mm. x 1.'3 mm., postical '75 mm. x '5 mm., antical
I'G mm. X 1' ram., postical '8 ram. x 'G mm.; bracteole I 'l mm. x
1' mm. ; periantli 3' mm. x 2'5 mm., teeth at the mouth '1 nim.
long x '1 mm. broad, at the base '075 mm. x '05 mm., '05 mm. x
'05 mm. ; pistillidia '225 mm. x '06 mm. ; valves of capsule
1'15 mm. X '6 mm.; spores '055 mm. x '045 mm. ; elaters '2 mm.
X '0125 mm.; male catkin 2' mm. x 1'25 mm. ; perigonial bract,
antical lobe I 'l mm. x '75 mm., postical '6 mm. x '5 mm. ; perigonial
bracteole '5 mm. x '4 mm. ; antheridia '85 mm. x '3 mm,
H a b .—In large patclies on stones, rocks, and trees, often
common, especially in limestone districts. Fruit somewhat rare-
1 to 3, 5 to 18. I,
Found on the Continent and in North America.
Obs.—This is the commonest of the British Porella;, for distin-
guisliing cliaracters of which see notes under the other species. I t
quickly discolours water upon immersion.
D escription of P late XXX.—Fig. 1. Plant natural size
(Engl. Bot.). 2. Portion of brancli, antical view x 11 (C. and P.
n. 71). 3. Portion of stem, postical view x 11 (ditto). 4-6.
Leaves X 11 (ditto). 7. Lobule of leaf x 16 (ditto), 8. Portion
of leaf X 290 (ditto). 9,10. Stipules x 16 (ditto). 11. Sub-bract
X 24 (Sweden, S. 0. Lindberg). 12, 13. Bracts x 16 (ditto).
14. Bracteole x 16 (ditto). 15. Perianth x 11 (ditto). 16. Portion
of tlie mouth of periantli x 85 (ditto). 17. Male catkin x 16
(ditto). 18. Perigonial bract x 16 (ditto). 19. Perigonial bracteole
X 24 (ditto). 20. Antheridium x 24 (ditto).
4. P orella riv u la ris {Nees), Lindb.
Madotheca rivularis, Nees, Nat. Eur. Leb. 3, p. 196 (1838).
Porella rivularis (Nees), Lindb. Muse. Scand. p. 3 (1879).
Dioicous, depresso-ciespitose, medium to largish in size,
varying in colour from pale to dark olive or brownish-green, when
dry often yellowish-green. Stems irregularly pinnate or subdichotomous,
apices often suhfastigiate, somewhat firm, frontally
compressed, 15 x 20 cells in diameter; cortical cells very small 1-3,
outer rows reddish-brown, inner much larger, hyaline. Leaves
approximate, slightly appressed, incubous, horizontal or horizontal-
patent-divergent, unequally bilobed, antical lobe much the larger,
almost plane, obliquely rotund-ovate, apex slightly decurved,
margin distantly denticulate or subentire, usually with 1-3 large
teeth at the antical base; postical lobe or lobule erect or erecto-
patent, contorted, much deourrent, obliquely ovate or ovate-
lanceolate, acute, sometimes uncinate, margin recurved, undulate,
repand, subentire or denticulate, often with few large teeth near the
liase; texture somewhat thin hut firm, epidermis dull, rarely with
a sliglit polish, cells medium size, roundish, walls thin, trigones
very distinct. Stipules appressed to stem or slightly recurved,
very decurrent, quadrate-oval, apex rotundate, margin reflexed,
undulate, repand, subentire or dentate, especially at the base.
Flowers ? produced on short lateral branches, nearer the postical
tlian tlie antical side of stem ; bracts about 3 times smaller than
the leaves, unequally bilobed, antical lobe oval, apex acute, margin
entire, postical lobe aliout half the size, quadrate-oval, margin
quite entire; bracteole small ovate-quadrate, retuse, margin quite
entire. Perianth broadly oval, complánate, mouth small, subentire.
Pistillidia about 8. Andrcecia on short lateral branches,
small; perigonial bracts closely imbricate, 4, 5 pairs, unequall}'
bilobed, complicate-concave, antioal lobe oval-oblong, margin
entire, postical lobe half the size, oblong-quadrate, margin quite
entire. Antheridia oval.
D imensions.—Stems to 2 inches long, '4 mm. to '5 mm. in
diameter, with leavms 4' mm. wide; leaves, antical lobe 2'25 mm.