204 PLANT MORPHOLOGY 



ferentiatctl into an upper annulus, consisting of several series of large 

 thin-walled cells, and a lower rim. When the capsule is mature, the 

 annulus collapses and the operculum comes off, exposing the peristome. 

 This consists of one or two rings of tooth-like projections that are 

 anchored to the rim. The usual number of teeth is 16, but they may 

 occur in some other multiple of 4. The teeth, which are hygroscopic, 

 assist in spore dispersal, bending inward and outward. In a few genera. 



Fig. 168. Longitudinal section of the upper part of the capsule of Mnium, showing the 

 operculum and two teeth of the peristome, X 90. (After Chamberlain.) 



said to be "cleistocarpous," an operculum and a peristome are lacking, 

 the capsule wall rupturing irregularly in dehiscence. In the other genera, 

 which are "stegocarpous," an operculum and a peristome are present. 



Often the lower portion of the capsule does not produce spores, but 

 forms a chlorophyll-bearing region, called the apophysis, in which stomata 

 are present (Fig. 167). In many mosses the apophysis is ring-like. The 

 seta of mosses is nearly always very long. It has a central strand of 

 elongated cells, but these are not conductive in function. The foot is 

 simple. 



Summary. The Bryales are the most highly developed group of bryo- 

 phytes. The gametophyte consists of a protonema giving rise to a leafy 

 shoot, the latter being differentiated in form and somewhat in structure. 

 The antheridia are terminal and club-shaped, developing by means of a 



