MUSCI. , ^6"] 



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. 



The 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, B). 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 Airichum and other Polytri- 

 chaceae, the stouter rhizoids coil round one another like 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 Reproduction 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, A,p). In some species {Mnium, 

 Bryum, Barbuia, &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 Phascum, 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. 



