MOSSES. 



3^3 



(2) T/ie Sexual Genera /ion, i.e. the leaf-bearing plant which afterwards pro- 

 duces the sexual organs, originates from the lower cells of the lateral branches of 

 the protonema ; the apical cell of an elongated protonema-filament does not appear 

 ever to become transformed so as to give rise to the leafy plant. Where a leafy 

 plant is about to be produced, a short tube is formed from one of the lower cells, 

 which, after being partitioned off, is divided by one or two more transverse septa ; 

 its apical cell thus becomes the apical cell of a bud, becoming divided by rapidly 

 succeeding walls which intersect in opposite directions. In the Sphagnaceae the 

 bud arises in a similar manner from a marginal cell of the flat pro-embryo ; in 

 Tetraphis from the narrow base of a marginal cell ; in Andreaea from lateral cells 

 of the various kinds of pro-embryo except the leaf-like form. The cells cut off 

 by the first oblique divisions are the first segments of the young stem, which either 

 develope at once into leaves, or undergo only the first divisions into leaf-forming 

 segments. Articulated rhizoids, which grow at once downwards, usually arise from 

 these first segments after they have previously divided, and enable the young plant 

 to take root. 



I-IG. :j;7.— Production of rhizoids from the protonema of M>tium hornuni. with leaf-forming buds A'; 

 ■w-w the root-hairs of an inverted sod, from which shoot protonema-filaments « n (xgo). 



The apical cell of the stem is wedge-shaped 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 bottom surface turned upwards (Fig. 106, p. 132). 

 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 

 now 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 \, the segments themselves lying 

 here in three straight rows with the ^ arrangement, because each newly formed 

 transverse wall is parallel to the last but three (both belonging to one segment). 

 In Polytrichum, Sphagnum, Andreoea, &c., on the other hand, each new primary 

 wall encroaches on the ascending side with regard to the leaf-spiral ; the transverse 

 walls of each segment are not parallel ; the segments themselves do not lie, even 



