308: Structural and Physiological Botany. | 
a. Acrocarpi. The theca springs from the apex of the main: 
stem or its branches ; e.g. Funaria, Splachnum, Dicranum, > 
Bryum, Polytrichum, &c. (Figs. 427, 432, 433). | 
6. Fleurocarpt. ‘The theca springs from the axil.of a leaf; 2. 
Hypnum, Fontinalis, &c. (Figs. 434, 435). 
c. Lnthophyllocarpr. The lateral or terminal theca springs from 
a duplication of the leaves, 
Mosses are generally distributed over the surface of the earth ; only 
a few grow in water. They are of no economical importance; the 
species of Sphagnum contribute largely to the formation of peat. 
Cuass VIL.* Filzces: 
Ferns have usually a simple or branched creeping: rhi- 
zome, either below or above the surface (Fig. 436) ; rarely. 
an erect woody stem, which is then always simple (Fig. 437). 
In either case the stem always continually dies off slowly at 
its lower end, or becomes lignified. Large numbers of ad- 
ventitious roots provided with root-hairs break out from the 
lower part of the stem or from the rhizome, while the upper 
part frequently puts out aérial roots. The stem is covered, 
when young, with an epidermis provided, where above- 
ground, with stomata. ‘The subjacent cortical tissue either 
consists entirely of thin-walled parenchymatous cells, or be- 
comes differentiated into an outer cortex consisting of thick- 
walled cells, and a thin-walled parenchymatous inner cortex 
(Fig. 438 R’ and R”), the latter passing over gradually into — 
the fundamental tissue. The activity of the cambium of 
the vascular bundles is limited, as also is their diametral 
growth, the vascular bundles growing chiefly at the apex.: 
The bundles of the entire plant are in direct communication 
with one another above and below, and thus form a system 
of fibro-vascular bundles. ‘They divide and ramify in the 
stem, forming a complete network, and send out branches 
into the leaves. In the roots, on the contrary, the bundles 
coalesce into a single central or axial vascular bundle. The 3 3 4 | 
separate bundles, as seen in transverse section, are some-_ 
times roundish and sometimes ribbon-shaped, and are 
