MUSCI. , '^6^ 



Funan'a, Bartramia, Mnium, Bryum, and others) ^ In PoIyirichu?n, Atrichum, and 

 Dawsonia alone do decided thickenings of the cell-walls take place in the central 

 bundle in such a manner that each of several groups of originally thin-walled cells 

 becomes surrounded by a thick wall and they 

 together form the bundle. In Polytrichum 

 vnmune there are found similar thinner extra- 

 axial bundles. Sometimes bundles of thin- 

 walled cells run from the base of the leaf- veins 

 obliquely downwards through the tissue of 

 the stem as far as the central bundle, which 

 Lorentz regards as foliar bundles {e.g. in 

 Splachnum luteum, Voiiia nivalis^ &c.). If it 

 is borne in mind that in some vascular plants 

 fibro-vascular bundles of the most simple 

 structure occur, and if the similarity of the 

 cambiform cells of true fibro-vascular bundles 

 to the tissue of the central and foliar bundles ^'^- '''■;::S^':^::S^!St^''''"^""' 

 in Mosses is considered, these latter may with- 

 out doubt be held to be fibro-vascular bundles of the simplest kind. 



As has already been mentioned, the leaf originates from the broad papillose 

 bulging of a segment of the apical cell of the stem : this is cut off by a wall. The 

 lower (basal) part is concerned in the formation of the outer layers of tissue of 

 the stem, whereas the apical part of the papilla constitutes the apical cell of the 

 leaf; it forms two rows of segments by walls perpendicular to the surface 

 of the leaf and inclined to the right and left. The number of the segments to 

 be formed, in other words, the terminal growth of the leaf, is limited, and the 

 formation of tissue from the cells thus formed advances downwards, ceasing finally 

 at the base. The whole of the tissue of the leaf is sometimes (as in Fontinalis) 

 a simple layer of cells; but very commonly a vein, i.e, a more or less broad bundle, 

 is formed from the base towards the apex, dividing the unilamellar lamina into 

 right and left halves, and consisting itself of several layers of cells. The vein is 

 sometimes composed of uniform elongated cells, but more often various forms of 

 tissue become differentiated in it, among which bundles of narrow thin-walled cells 

 similar to the central bundle of the stem frequently occur, and these are sometimes 

 continued to it through the external tissue of the stem as foliar bundles {cf. Lorentz, 

 /. f.). The shape of the leaves of Mosses varies from almost circular through broadly 

 lanceolate forms to the acicular ; they are always sessile and broad at their insertion ; 

 usually densely crowded ; only on the stolons of some species, the pedicels of the 

 cupules of the gemmae of Aulacomnion and Tetr aphis, as well as at the base of 

 some leafy shoots, do they remain small and remote (cataphyllary leaves). In the 

 neighbourhood of the reproductive organs they usually form dense rosettes or buds, 

 and then not unfrequently assume special forms and colours. In Racopilum, Hypo- 

 pierygium, and Cyathophorum, there are two kinds of leaves, a row of larger upon 



' It is stated by Lorentz that the seta of the sporogonium is always provided with a central 

 bundle of this kind. 



