3^4 



MUSCINEM. 



when first formed (without the assistance of any torsion of the stem), in three 

 straight rows, but in three parallel spiral lines winding round the axis of the stem 

 one above another; and the consecutive segments and their leaves diverge at an 

 angle which, from what has been said, must be greater than ^ ; the phyllotaxis is 

 •f, I, and so on \ 



The primary meristem of the stem situated beneath the punctum vegetationis 

 which passes over into permanent tissue usually becomes differentiated into an inner 

 and a peripheral mass of tissue, which are not generally sharply defined ; the cell- 

 walls of the peripheral and especially of the outermost layers are usually strongly 

 thickened and of a bright red or yellowish red colour ; the cells of the inner funda- 

 mental tissue have broader cavities and thinner walls more slightly or not at all 

 coloured. In some INIoss-stems this differentiation goes no further than into an 



outer skin consisting of several layers and a 

 thin-walled fundamental tissue {e. g. Gymno- 

 stovium rupestre, Leucobryiim glaucum, Hed- 

 wigia ciliata, Barbiila abides, Hylocoiniuni 

 splendens, &c., according to Lorentz) ; while 

 in many other species a central bundle of 

 very thin-walled and very narrow cells is 

 formed in addition (Grimmia, Funaria, Bar- 

 tramia, Mnium, Bryum, and others)^. In 

 Polytrichum, Atrichum, and Dawsonia alone 

 decided thickenings of the cell-walls take 

 place in the central bundle and in such a 

 manner that numerous groups of cells,*origin- 

 ally thin-walled but each group itself sur- 

 rounded by a thick wall, form the bundle. In 

 Polytrichuvi commune there are found also 

 similar thinner extra-axial bundles. Some- 

 times 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 Splachniim luteum, Voitia nivalis, &c.). 

 If it is borne in mind that in some vascular plants fibro-vascular bundles of 

 the most simple structure occur, and the similarity of the cambiform cells of true 

 fibro-vascular bundles to the tissue of the central and foliar bundles in Mosses is 

 considered, these latter may without 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 cell of the stem which is separated by a longitudinal partition ; a lower 



Fig. 228.— Transverse section of the stem of Bryi 

 roseum, with root-hairs iv (X90). 



* If the position of each fourth division of the apical cell is kept in view, it gives the impression 

 as if the apical cell rotated slowly on its axis, producing, at the same time, leaf-forming segments, 

 (Compare on this subject the work of Leitgeb mentioned above, Lorentz's work, Hofmeister's Mor- 

 phologic, p. 194, and MuUer, Bot. Zeitg. 1869, pi. VIII.) 



^ It is stated by Lorentz that the pedicel of the sporogonium is always provided with a central 

 bundle of this kind. 



