VII THE BRYINEyE 209 



two or three layers of cells, large hyaline ones, somewhat as in 

 Sphagnum, and small green cells. The hyaline cells, as in 

 Sphagnum, have round holes in the walls, but no thickenings. 

 The midrib may be narrow, as in Funaria, or it may occupy 

 nearly the whole breadth of the leaf, as in the Polytrichaceae, 

 where, owing to the almost complete suppression of the lamina, 

 secondary vertical plates of green cells are formed (Fig. 107, B). 



The one-third divergence of the leaves found in Fontinalis ^ is 

 replaced in most other genera by a larger divergence.^ Thus 

 in Funaria Jiygrometrica it is -| ; in Polytrichum commune ^^ ; 

 in P. formosum -^-|. 



As the archegonia are borne upon lateral branches, or upon 

 the main axis, the stegocarpous Bryineae are frequently divided 

 into two main divisions, the Pleurocarpse and the Acrocarpae, 

 which are in turn divided into a number of subdivisions or 

 families. How far the division into acrocarpous and pleuro- 

 carpous forms is a natural one may be doubted, as probably the 

 latter is secondary, and it is quite conceivable that different 

 families of pleurocarpous forms may have originated inde- 

 pendently from acrocarpous ones. 



The simplest of the stegocarpous Mosses, while having the 

 operculum well marked, have no peristome. Thus the genus 

 Gymnostomum has no peristome at all, and in an allied genus, 

 Hymenostomum, it is represented by a thin membrane covering 

 the top of the columella. In nearly related genera, however, 

 e.g. Weisia, a genuine peristome is present. 



The Tetraphideae, represented by the genus Tetraphis (Fig. 

 105), are interesting as showing the possible origin of the 

 peristome, as well as some other interesting points of structure. 

 Tetraphis pellucida is a small Moss, which at the apex of its 

 vegetative branches bears peculiar receptacles containing multi- 

 cellular gemmae of a very characteristic form. The leaves that 

 form the receptacle are smaller than the stem leaves, and 

 closely set so as to form a sort of cup, in which the gemmae are 

 produced in large numbers. These arise as slender multi- 

 cellular hairs, the end cell of which enlarges and forms a disc, 

 at first one-layered, but later, by walls parallel to the broad 

 surfaces, becoming thicker in the middle, and lenticular in form. 

 The arrangement of the cells in the young gemmae looks as if 



^ This seems to be strictly the case only in the smaller branches ; in the larger axes 

 the leaves are not exactly in three rows. ^ Goebel (8). 



P 



