nate, obliquely inclined septa, a leaflet is produced composed o f a few
large quadrate parenchym cells filled with a slimy fluid containing
chlorophyl g ran ule s; but with the appearance o f the fifth leaflet
begins the differentiation into two kinds of cells so characteristic of
the Sphagnacece.
T h e lea f becomes marked out into a system o f square cells,
each of which is surrounded by four oblong c e lls ; in the latter
chlorophyl granules rapidly increase in number and size, while the
former lose all colouring matter from their contents and keep
enlarging at the expense o f their protoplasm; then the fibres are
deposited on their internal walls, first as fragmentary rings which
afterwards coalesce into complete rings or sp ira ls ; and lastly,
small scattered rings appear on the internal surface, the membrane
enclosed by which becoming resorbed, there result the well-known
pores or foramina so generally present in the branch leaves o f these
plants, through which it is not uncommon to find infusoria have
passed, for we may see them sporting about in the interior o f the
cell.
Hedwlg had noticed the beautiful structure o f the Sphagnum
leaf, for in his Fundamenta Hist. N a t. Muscorum, i. p. 25 ( i 782), he
mentions the large areolee, void o f chlorophyl, traversed by ve ry
fine vessels containing parenchyma, which he suggests may correspond
to the ducts o f flowering plants.
Moldenhawer, however, detected the true nature o f the areolation,
and the two kinds o f cells of which it is composed, with the
presence o f threads and pores in the vesicular cells, and Von
Mohl still further extended his researches.
T h e leaves o f all Sphagna consist o f a single stratum o f cells
without any midrib, and these cells are o f two distinct kinds
alternating with each other; ist, narrow chlorophyllose cells
{ductus intercellulares o f C. Müller, interstitia o f Hampe), which
form a frame or network o f somewhat bent hexagonal meshes,
and usually six o f these cells enter more or less into forming the
boundary o f each mesh, their colour being green, yellow, or red,
according to that o f their contents ; these cells are really the most
important part o f the leaf, since they carry on the vital functions,
and form the scaffold on which the hyaline cells are stretched :
2nd, large colourless vesicular cells dropped as it were into each
mesh o f the network, and containing in nearly all species spiral
fibrils on their internal wall and perforated with foramina; for
these cells Mr. Mitten uses the term spatia or spaces. This
description applies to the leaves o f the branches, but in those of
the stem and perichaetium the two kinds o f cells are not so distinct,
as the chlorophyl is wanting and the hyaline cells are often
extremely narrow, especially those at the margin, where they
generally form a more or less wide border.
T h e stem leaves in all the European Sphagna differ considerably
from the branch leaves both in form and structu re ; they are
distant from each other, with a | arrangement, or five leaves in two
spiral turns, and are generally reflexed against the stem, as if
pushed back by the descent o f the pendent branches. T he ir form
is oblong, ovate, or Ungulate, and at their basal angles there
are generally present more or less evident auricles ; they are also
very uniform on the same plant both in size and shape. T h e
areolation is laxer than that o f the branch leaves, and spiral fibres
are rarely present in their hyaline c e lls ; the basal cells form one
or more rows o f incrassate vesicular cells, more or less coloured,
but the greater part o f the lea f is colourless from the absence o f
chlorophyl in the narrow cells.
T h e branch leaves are small and closely imbricated, and differ
considerably on the two kinds o f branches, and even on different
partá o f the same bran ch; on the divergent branches they are
small at base, becoming larger in the middle o f the branch, and
narrower and more distant towards the p o in t; the three or four at
the extreme base o f the branch are ve ry small and have a peculiar
shape, being somewhat obliquely triangular in outline, and partly
resemble the stem lea f in areolation ; in fact, they convey the idea
o f one half o f a stem le a f which has been split down the middle, and
possibly may originate by being torn apart by the separation o f the
branches forming the fascicle, at their first stage o f development.
Russow attaches importance to these leaves, and names them
intermediate leaves, but they are not always alike in the same
species, nor do the y offer much variety in different species, and
they have always a broad border o f narrow cells ; the leaves o f the
pendent branches are all longer and narrower, as are also their
component cells.
T h e relation o f the two forms o f cells to each other, in the
anatomy o f the ramuline leaves, is a point o f great importance,
since it originates in the fundamental formation o f the leaf, and it
therefore takes part in the diagnosis o f species ; to observe this
c