PLAGIOCHILA. 453 
fertilisation and maintain the plants in perpetual sterility. The leaf- 
suckers empty the cell from which they arise, and often several adjacent 
cells, of chlorophyl. When the parent leaf is entirely decayed, the suckers 
that survive start off on a separate existence, and speedily assume the 
normal foliage of the species. Lining the roof of a cavern at the foot of 
the voleano Tunguragua I found a matted growth of leaf-suckers, bearing 
minute bifid or trifid leaves, and differing greatly from those of the parent 
plant, which is what I have called Pl. hypantra n. sp. Pl. macrifolia 
Tayl., in the Cinchona forests on the western slope of Chimborazo, and 
several other species occasionally put forth leaf-suckers. Nor is it only 
in the genus Plagiochila that these structures exist. Forty years ago, in 
the “Phytologist” for February, 1845 (vol. ii. p. 85), I described and 
figured the way Herberta adunca (Dicks.)—then called, but incorrectly, 
Jung. juniperina Sw.—puts forth minute adventitious ramuli from the 
surface of its leaves; and I have since then noted them in nearly every 
genus of hepatice, even in Lejeunea and Frullania. To whatever genus 
the mother-plant belongs, the leaf-suckers have always minute bifid 
leaves, so like those of a Cephalozia or Jungermania, that I suspect several 
supposed “species” of Jungermania, described in books from sterile 
frustula, found “intermixed with” or “growing upon” other and larger 
species, to be in reality mere leaf-suckers of those species. 
The characters of Plagiochila are so marked and peculiar that the 
genus cannot be confounded with any other. The perianth of Letoscyphus 
is similarly flattened at the sides, and truncate at the apex, but the 
opposite leaves are always connate with the large intervening underleaves, 
whereas the opposite-leaved Plagiochile never have any underleaves, 
those organs being confined to a few of the alternate-leaved species. 
Moreover the procumbent stems of Leioscyphus are always conspicuously 
radicellose, and the branches are distinctly postical, axillary to the under- 
leaves.—In the very rare cases where the perianth of Plagiochila becomes 
trigonous, by the addition of a narrow postical face, there are always the 
radicellose stem of Lophocolea, the large and conspicuous underleaves, the 
tristichous involucres of large bifid bracts, and the 3- or 6-lobed mouth 
of the perianth to distinguish the latter genus. 
The arrangement of species propounded by Lindenberg in his admirable 
monograph I have found in practice so intractable that I here propose 
another, which I hope may be found easier to work with, and more 
conformable to nature. With the full description of the genus I have 
already given, and the characters of the sections to follow, the student 
will need no further explanation. Besides the five sections here specified, 
a sixth (of which I found no example in my American travel) would be 
needed to contain a few species, including our Pl. asplenioides, the New- 
Zealand Pl. gigantea, and some others, which have large alternate leaves, 
long tubular perianths, and above all an elongated pedicel, sometimes 
exceeding an inch, whereas in all the other sections the pedicel is 
shortened down to at most twice the length of the perianth. 
Divisio I. CAULIFLORA, 
Caules e caudice prostrato assurgentes, erecti pendulive, 9 vulgo inno- 
vando-ramosi et vix aliter divisi, se. apice florentes et e foliorum involu- 
cralium axillis innovationem hine vel utrinque proferentes, innovationibus 
vel simplicibus vel denuo (sepe iteratim) mnovandis. 
TRANS, BOT. SOC. EDIN. VOL. XV. 3D 
