1868.] 



BRA1THWAITE — ORGANIZATION OF MOSSES. 



473 



of forms (figs. 24, 25, 26). They consist of two strata of cells, 

 the outer in two rows, transversely jointed (trabeculate), richly 

 coloured, and often separated for a part of 

 their length, in the central or divisural 

 line ; the inner in one row, thin and hygros- 

 copic, and projecting inward as transverse 

 lamellae (figs. 22, 23, 27). In the Poly- 

 trichaceae, however, they are quite different, 

 and consist of a mass of agglutinated filaments, and Mr. Mitten 

 uses this distinction to separate all mosses into two sections, 



Fig. 23. Transverse sec 

 tion of tooth of outer 

 peristome. 



Fig. 24. Fruit of Tetraphis Fig. 25. Splachnum sphaericum, 



pellueida, peristome of with eight bigemiuate teeth, 



four teeth. and exserted columella. 



Arthrodonti, those with jointed teeth, and Nematodonti, those with 

 filamentous teeth. In the Polytricha, also, the top of the colu- 

 mella is dilated into a membrane, closing the mouth of the 

 capsule, and joined to the points of the teeth ; this expansion has 

 leen named the epiphragm or tympanum (fig. 27). 



Fig. 26. Bifid tooth from 

 peristome of Fissidens, 



Fig. 27. Peristome and tympanum 

 of Pogonatam aloides. 



