MUSCI. 



169 



itself, and springs from an almost sheathing base. The tissue of the leaf, apart from 

 the nerve, is for the most part uniform and composed of cells containing chlorophyll 

 which sometimes have papillose projections on the surface ; in the Sphagnaceae and 

 Leucobryaceae it is differentiated into cells containing air, and green cells with watery 

 contents, and these are definitely arranged in the leaf. 



The branching of the moss-stem appears never to be dichotomous, but it is at the 

 same time probably never axillary though not without relation to the leaves, and even 

 where the branching is copious the lateral shoots are usually much fewer in number 

 than the leaves. In many cases the growth of the lateral branches is distinctly limited, 

 and this leads occasionally to the formation of branch-systems with definite forms and 

 a resemblance to pinnate leaves, as in Thuidium and Hylocomium. When the primary 

 axis produces sexual organs at its apex, a strong lateral shoot from beneath it often 

 continues the vegetation, and these innovations lead to the formation of sympodia. 

 A not infrequent form of shoot is 

 the stolon which, without leaves or 

 with only small leaves, runs along or 

 beneath the ground and eventually 

 rises into the air and produces erect 

 fully-leaved shoots. The branching 

 is as a rule very various and closely 

 connected with the mode of life. The 

 morphological origin of the lateral 

 branches has been carefully examined 

 and excellently described by Leitgeb 

 in Fontinalis and Sphagnum. Later 

 researches into the same point in 

 Hypnum, Schtstotega, and Fissidens 

 show that his results may be accepted 



aS generally true. It is agreed that FIG. 122. Longitudinal section through the apical region of a young 



, , .. , . , . , stem of Fontinalis antipyretica ; -v apical cell producing three rows of 



the mOther-Cell, Which IS at the Same segments which are indicated by stronger lines. Each cell divides first by 



, i ii r u t- a wal1 a (teaf-wall) into an inner and an outer cell ; the inner cell produces 



time the apical Cell, OI a branch IS a portion of the inner tissue of the stem, the outer cell the cortex of the 



- , , . , . P , - stem and a leaf. After Leitgeb. 



formed beneath the leaf and from 



the same segments as the leaf (Fig. 122); in Fontinalis the branch is formed beneath 

 the median plane of the leaf, in Sphagnum beneath the kathodic half of the leaf; in 

 consequence of the further development of the mother-shoot the lateral shoot appears 

 later to stand in Sphagnum by the margin of an older leaf, and in this way we may 

 explain the earlier statement of Mettenius, that the lateral shoots in Neckera complanata^ 

 Hypnum triquetrum, Racomitrium canescens and other species, are placed beside the 

 margins of the leaves. If the shoot arises beneath the median plane of a leaf, the 

 arrangement of the leaves in straight rows and the further growth of the stem may 

 make it seem as though the shoot had originated above the median plane of an older 

 leaf, that is in the axil of a leaf. Leitgeb states that articulated hairs are formed in 

 the genera mentioned above in the axils of the leaves, or perhaps rather on the upper 

 surface at the base of the leaves. 



There is a considerable difference between the maximum and minimum of length 

 in the leafy axes and systems of axes in the Mosses ; the simple stem of the Phascaceae 



