3^4 
MUSCINEM. 
mother-cells of leaves which at once grow out into expanded leaves instead of 
into filamentous structures. This interpretation is confirmed by all possible tran- 
sitional forms, and a comparison of the ordinary characteristics of the stem and 
of the protonemal filament at once demonstrates its truths Whether or not the 
Andreseacese, Sphagnese, &c. resemble the Bryineae in this feature, and the extent 
of such a resemblance, must be decided by future researches. 
The apical cell of the stem is two-sided in Schistostega and Fissidens, and 
produces two straight rows of alternating segments ; in the rest of the Mosses it 
is a three-sided pyramid, with the basal surface turned upwards (Fig. ii6). Each 
segment of the apical cell arches outwards and upwards as a broad papilla; this 
is cut off by a longitudinal wall (which Leitgeb calls a foliar wall), and developes, 
by further divisions, into a leaf, while the lower inner part of the segment produces, 
by further divisions, part of the inner tissue of the stem. Since each segment 
forms a leaf, the phyllotaxis is determined by the position of the consecutive 
segments. In Fissidens two straight rows of alternate leaves are thus formed ; in 
Fontinalis three straight rows with the divergence J, the segments themselves lying 
here in three straight rows with the J arrangement, because each newly formed 
primary wall is parallel to the last but three (both belonging to one segment). 
In Polytrichum, Sphag7iu?n, Atidrecsa, &c., on the other hand, each new primary 
wall encroaches on the ascending side with regard to the leaf-spiral ; the primary 
walls of each segment are therefore not parallel ; the segments themselves do not 
lie, even 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 J ; the phyllo- 
taxis is f , |, and so on ^, 
The primary meristem of the stem, situated beneath the punctum vegeiationis, 
passes over into permanent tissue and 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 Moss-stems this differentiation goes no further than into an 
outer skin consisting of several layers and a thin-walled fundamental tissue {e.g. 
Gymfiostomum rupesire, Leucohryum glaucuin, Hedwigia ciliata, Barbula abides, Hylo- 
comium 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, 
^ I must content myself with the above brief account, for Herr Schuch has not yet published his 
observations which I had the opportunity of following in all their details. Herr Müller is at present 
(1874) working at this subject, but is not yet in a position to publish his results. Figs. 247 and 248 
were drawn at a time (1866) when the views expressed above were unformed. (See Arb. d. bot, Inst, 
in Würzburg, Heft IV, 1874,) 
^ 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- 
phologie, p. 194, and Müller, Bot. Zeitg. 1869, pi. VIII.) 
