366 MUSCINEM, 



one side, and a row of smaller leaves upon the other side of the stem. The 

 leaves are not branched, but entire or toothed, rarely slit. In some kinds peculiar 

 outgrowths are formed upon the inner or upper surface of the leaves ; in Barbula 

 abides articulated capitate hairs. The lamina, which in other cases expands 

 right and left from the median plane, is, in Fissidens, expanded in the median 

 plane itself, proceeding from an almost sheathing base. The tissue of the leaf is, 

 with the exception of the central vein, usually homogeneous and composed of 

 cells containing chlorophyll, which sometimes project above the surface as mamillse ; 

 in the Sphagnaceae and Leucobryum the tissue is differentiated into cells containing 

 air, and others which contain sap and chlorophyll, arranged in a definite manner. 



The mode of branching of the stem of Mosses is apparently never dichotomous, 

 but also probably never axillary, although connected with the leaves. Even when 

 the branching is copious the number of lateral shoots is nevertheless usually much 

 smaller than that of the leaves ; in many cases the lateral branches are definitely 

 limited in their growth, leading sometimes to the formation of definite ramified 

 systems similar to pinnate leaves {Thuidium, Hylocomiuni). When the primary 

 shoot produces reproductive organs at the summit, a lateral shoot situated beneath 

 it not unfrequently displays a more vigorous growth, continuing the vegetative 

 system; and by such innovations sympodia are formed. It sometimes happens 

 that stolons, that is shoots either destitute of or furnished with very small leaves, 

 creep on or beneath the surface of the ground, elevating themselves at a later period 

 as erect leafy shoots. The mode of branching is very various, and is closely con- 

 nected with the mode of life. The morphological origin of the lateral shoots has 

 been carefully investigated by Leitgeb in the case of Fontinalis and Sphagnum^ and 

 admirably described. Since these two genera belong to very different sections, the 

 results obtained in this case may be considered as of general application to the 

 whole class. They agree in the fact that the mother-cell (which is at the same 

 time the apical cell) of a branch originates beneath a leaf from the same segment 

 as the leaf (Fig. 116). In Foniinalis the branch arises beneath the median line 

 of the leaf; but in Sphagnum beneath its cathodal half. In consequence of the 

 further development of the mother-shoot, the lateral shoot in Sphagnum appears at 

 a later period to stand by the side of the margin of an older leaf; and this is 

 probably the explanation of the earlier statement of Mettenius that in Neckera 

 complanata, Hypnum tn'queirum, Racomitrium canescens, and others, the lateral shoots 

 stand by the side of the margins of the leaves. When the shoot arises beneath 

 the median line of a leaf, and the leaves are arranged in straight rows, the further 

 growth of the stem may cause it to seem as if the shoot originated above the 

 median line of an older leaf, in other words as if it were axillary. Leitgeb states 

 that articulated hairs arise in the genera named in the axils of the leaves, or perhaps 

 more correctly at the base of the upper surface of the leaves. 



The dimensions attained by the leaf-bearing axes and axial systems of Mosses 

 show a wide range. In the Phascacese, Buxbaumiay and others, the simple stem 

 is scarcely i mm. in height ; in the largest species of Hypnum and Polytrichum 

 it is not unfrequently 2,' 3, or more decimetres in length, and, if belonging to 

 more than one axis, even longer, owing to the formation of innovations and sympodia 

 {Sphagnum). The thickness of the stem is less variable ; yV mm. in the smallest, 



