MUS CI. 
it scarcely exceeds i mm. in the thickest forms. Its dense tissue, coloured exter- 
nally, is however very firm, often stiff, always very elastic, and capable of offering 
long resistance to decay. 
T/ie Root-hairs (Rhizoids) play an extremely important part in the economy 
of Mosses. It is only in the otherwise very abnormal section of the Sphagnacese 
that they are very sparsely and poorly developed; in most other forms they occur 
in large numbers at least at the base of the stem, often clothing it completely with a 
dense reddish-brown felt. Morphologically the rhizoids are not sharply distinguished 
from the protonema ^ ; and it will be seen further on that they, like it, are capable 
of forming new leafy stems. They arise as tubular protuberances from the superficial 
cells of the stem, elongate by apical growth, and are segmented by oblique septa ; 
at the growing end the wall is hyaline, and particles of earth become attached 
to it in the ground; subsequently these fall off; the wall becomes thicker and 
brown, as is also the case with the aerial root-hairs. The cells contain a 
considerable quantity of protoplasm and drops of oil (Fig. 250, E). In many 
Mosses the root-hairs branch very copiously in the ground ; they often form a dense 
inextricable felt ; a felt of this kind may even arise above ground as a dense turf, 
and may serve as a soil for future generations. In Atrichum and other Polytri- 
chacese, the stouter rhizoids coil round one another Hke the threads of a rope, the 
branches which proceed from them doing the same, and only the last and finest 
ramifications remain free. 
The Vegetative Reproductio7i of Mosses is more copious and varied than is the 
case in any other section of the vegetable kingdom. It presents the peculiarity that 
the production of a new leaf-bearing stem is always preceded by the formation of 
a protonema, even when the propagation takes place by gemmae. Exceptions are 
afforded only by the few cases in which leaf-buds become detached and commence 
immediately to grow. ^ 
In describing the different cases in detail, the first point that must be brought 
prominently forward is that both the protonema which proceeds from the spore 
itself and the leafy stems which spring from it are capable of reproduction of 
different kinds. The original protonema is so far an organ of reproduction that it 
may produce upon its branches a smaller or larger number of leafy stems in 
succession or simultaneously ; sometimes the individual cells of the protonema- 
branch separate from one another after they have become rounded off into a 
spherical form, acquire thicker walls, and become for a time inactive (as in Funaria 
hygrometrica), forming, probably, at a later period again protonema- filaments. A 
secondary protonema may be formed from any root-hair when exposed to light in 
a moist atmosphere {cf. Fig. 247 and Fig. 250,^,/). In some species {Mnium^ 
Bryum, Barhiila, &c.) it is sufficient to keep a turf of Moss damp for some days 
and turned downwards, in order to produce hundreds of new plants in this manner. 
Some apparently annual species, e.g. of Phasciwi, Funaria, and Pottia, persist 
perennially by means of their root-hairs ; the plants disappear completely from the 
^ The rhizoids appear to be distinguished from the protonema only by the absence of chlo- 
rophyll and by their tendency to grow downwards ; the protonema developes certain branches as 
rhizoids ; and the rhizoids may, on their part, develope single branches as a protonema growing 
upwards and containing chlorophyll ; see p. 362. 
