~ stalked -‘sporogonium has a columella; [the elaters have no spiral 
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Special Morphology and Classification. . 301 » 
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bands] (Fig. 421, p. 296). 
3. MARCHANTIE&. The flat coriaceous thallus is branched di- 
chotomously [and possesses a mid-rib] ; the sporogonia are collected on 
a stalked organ or archegonial receptacle, and, burst, into four valves ; 
[they contain elaters] (Fig. 422, p. 297). & AS . 
4. JUNGERMANNIE@. [The vegetative structure is usually differ- 
entiated into a stem and distinct leaves]; the sporogonium bursts into 
four valves [and contains elaters] (Fig. 423, p. 298). 
The Hepaticze are distributed throughout the world, but are of no 
economical importance. 
Cisse: Vaio? A, Usct. 
The Musci or Mosses are nearly related to the Hepatice; 
but are in general of a higher type, no longer possessing any — 
of the characteristic features of Thallogens, but having a 
cylindrical stem covered with leaves (Figs. 427, 434). The  — 
stem of the order known as Sphagnacee is divided by nar-. 
row elongated cells, which are often lignified, into a central. 
large-celled axial and a looser cortical portion consisting of 
only a few cells (Fig. 426 1). True vascular bundles are 
altogether wanting ; but in most other families of Mosses 
there is n the centre of the stem an axis of simple struc- 
ture, which does not contain true vessels, but which is often 
described as a vascular bundle (Fig. 426 11.). This often — 
consists only of a few thick- or thin-walled cells. not sharply 
distinguished from the parenchyma of the stem, which serve 
for the conduction of the sap, and therefore perform the 
function of a vascular bundle. In some Mosses there are, 
however, cells with thicker walls, on which may be seen a 
very delicate spiral striation, and which therefore, altogether 
call to mind a vascular bundle. These are sometimes ~~ 
central; but sometimes, as in Polvtrichum, give place to’ 
a central medulla. Lateral branches from these bundles © 
sometimes pass into the leaves as veins. The leaves are 
often narrow, of very thin or even membranous texture, and 
