-64- 



ures is printed in the May number. In Fig. 15 the zig-zag- line shows plainly, 

 and in Fig. 17, the left hand side shows clearly the trabeculate inner face of 

 the tooth. The plates of lignin forming these thickenings are deposited on 

 both sides of the original wall as shown in Fig. 5, so that the teeth are 

 formed of a double layer of plates, Two rows on the outside and a single 

 row inside. The cells next inside the peristomial layer are much more num- 

 erous and somewhat irregular. They follow the curvature of the peristomial 

 cell walls forming a keel alternating with each cell as shown in Fig. 3. 



Fig, 2, A longitudinal section of a capsule of Mnium hornu7n x 500; a, 

 annulus ; b, outer peristome ; c, inner peristome. This section shows 

 clearly the method of formation of the double peristome. The teeth 

 of the outer peristome are formed by thickenings or " plates " laid down 

 on the inner and outer faces of the outer wall of a layer of cells extend- 

 ing around the capsule ; these thickenings are continued along the 

 top and bottom walls of these cells to form the transverse bars or trabe- 

 culse. The inner wall of this same layer of cells becomes thickened 

 to form the inner peristome 



Fig. 3 Shows one-fourth of a cross-section through the same capsule and 

 gives a good idea of the way the thickenings on the top and bottom 

 walls project into the cells, and of the keel-shape of the segments or 

 sections of the inner peristome. 



