THE BRYOLOGIST. 



Vol. V. September, 1902. No. 5. 



THE PERISTOHE. III. 



By a. J. Grout. 



There can be no doubt that there is no exact homology between the peri- 

 stomes of the Nematodonteae and those of the Arthrodonteae, for the teeth 

 of the former are composed of masses of cellular tissue while those of the 

 latter are composed of the thickened tangential cell walls (i.e., the cell walls 

 parallel to the walls of the operculum) of one or more layers of cells. The 

 joints or articulations from which this type of peristome takes its name are 

 the places of intersection of these tangential walls with the horizontal cell 

 walls forming the top and bottom of the cells. The rest of these horizontal 

 walls and the entire vertical radial walls (i.e., those forming the sides of the 

 cells) have been absorbed. If one were to take a pyramid consisting of a sin- 

 gle row of rectangular boxes of graduated sizes and after fastening one side 

 of them together in a straight line should knock away the other walls he 

 would get a good idea of the formation of the arthrodont peristome. A nar- 

 row strip of the tops and bottoms must be left between the remaining sides 

 to represent the articulations and the result would be comparable to only 

 one-half a tooth of the outer peristome of Hypnum. Then if both sides be 

 covered with a layer of plaster it will represent the thickenings laid on the 

 original cell wall to form the lamellae. 



While the arthrodont and nematodont types of peristome seem very dis- 

 tinct, there seems to be something of a connecting link in the peristomes of 

 the Buxbaumiaceae as typified by the peristome of Buxbauinia indusiata. 

 This peristome consists of an inner and an outer peristome, the inner of a 

 plaited cone, truncate and with a narrow opening at the top, apparently for 

 the gradual escape of spores, but Braithwaite quotes Zukal to the effect that 

 the spores cannot escape through this narrow opening. This may be so in 

 Buxbauinia^ I have not had sufficient suitable material to decide for myself, 

 but in the closely related Weber a sessilis the spores certainly are dispersed 

 through this narrow opening, though some of them may remain until the 

 capsule decays as in Buxbaumia. 



This inner cone is composed of a thin membrane made of the thickened 

 tangential cell walls of one of the layers of cells and is plaited or folded like 



B. indusiata: i and 2, peristome ; 3, pseudannulus (a) and peristome (b) in 

 vertical section, c, internal peristome; 4 and 5, teeth of external peristome: 6, 

 portion of the same more highly magnified ; 7-1 1, different transverse sections 

 of the teeth of the external peristome. D. foliosuin {Weber a sessilis): Di, 

 peristome magnified: D2, a single tooth; D3, vertical section of the peri- 

 stome, operculum, and capsule wall: D4, folds of the internal peristome in 

 transverse section. 



The July Bryologist was issued July ist, 1Q02. 



