MUSCI. 167 



segments and their leaves have an angle of divergence which must necessarily be 

 greater than one-third ; the phyllotaxis is in fact two-fifths, three-eighths, and so on. 



The primary meristem, which passes below the growing point of the stem into 

 permanent tissue, is usually differentiated into an inner and a peripheral mass of tissue, 

 and the limits of the two are as a rule not sharply defined. The peripheral layers, 

 the outermost especially, have their cell-walls usually much thickened and coloured 

 a bright red or reddish-yellow; the cells of the inner fundamental tissue have broader 

 cavities and thinner less highly coloured or colourless walls. The stems of some 

 Mosses have no other differentiation than this, viz. into an outer covering of 

 several layers of cells and a thin-walled fundamental tissue, for example, Gymnostomum 

 rupesire, Leucobryum glaucum, Hedivigia ciliata^ Barlula aloides, Hylocomium splendent 

 and others, according to Lorentz ; in many others, there is besides an axile bundle of 

 very thin-walled and very narrow cells, the central bundle, as in Grimmta, Funaria, 

 Bartramia, Mnium, Bryum, and many others ; it is only in Polylrichum, Atrichum^ 

 and Dawsonia that the walls of the cells of the 

 central bundle are strongly thickened. Bundles 

 of thin-walled cells sometimes run from the base 

 of the nerves of the leaves obliquely downwards 

 through the tissue of the stem to the central 

 bundle, the leaf-trace bundles of Lorentz ; such 

 are found in Splachnum luteum, Voitia mvalts, 

 Polytrichum, and others. If we remember that 

 vascular bundles of an extremely simple construc- 

 tion occur even in many Vascular plants, and 

 give due weight to the resemblance between the 

 cambiform cells of true vascular bundles and 

 the tissue of the central bundle and the leaf- 

 trace-bundles in the MoSSeS, We Shall Certainly FIG . 120 . Transverse section of the stem of 



be able to regard these bundles in Mosses as ru- ST 

 dimentary vascular bundles of a very simple kind. 



It has been already said that the leaf begins in a broad papillose protuberance of 

 a segment-cell of the stem, and that this protuberance is separated off by a wall ; a 

 lower, basilar part of this cell is employed to form outer layers of the tissue of the 

 stem, while the apical part of the papilla is the apical cell of the leaf, and forms two 

 rows of segments by dividing walls which are perpendicular to the surface of the leaf 

 and incline to the right and left. The number of these leaf-segments, in other words 

 the apical growth of the leaf, is limited, and when this growth ceases, the formation 

 of tissue from these segment-cells proceeds basipetally and finally ceases at the base. 

 The whole tissue of the leaf is sometimes, as in Fontinalis, a single layer of cells ; but 

 very often a nerve is formed running from the base toward the apex, that is to say a 

 bundle of varying breadth, which divides the one-layered lamina into a right and left 

 half, and is itself composed of several layers of cells ; its cells are sometimes uniform 

 and elongated, but different forms of tissue may appear in it, especially strands 

 of narrow thin-walled cells, which resemble those of the central bundle of the stem, 

 and are occasionally continued on to it as leaf-trace bundles. The outline of the 

 leaves of Mosses varies from almost circular through broadly lanceolate to acicular ; 



