26 HANDBOOK OF BRITISH MOSSES. 



form a short tuft of cottony threads. In Buocbaumiei the 

 outer peristome appears to be derived from the outer strata 

 of the walls of the sporangia, and not from the wall of the 

 intermediate space, and traces of the same structure may be 

 found in other Mosses, as Orthotrichum cupulatum (Plate 20, 

 fig. 4). 



In the more normal peristomes, the teeth vary in form, 

 length, sculpture, direction, connection, and many other points 

 which it is needless to enumerate here, as they are indicated 

 under each genus. These teeth, it may be observed, have not 

 the slightest homology with the leaves, and therefore none 

 with the petals of flowering-plants, being derived in a totally 

 different way. They are not in fact modifications of leaves, 

 but arise from the mere thickening of the walls of two contigu- 

 ous strata of cells. They are not like the leaves, arranged 

 spirally round the axis, but their bases are all in the same 

 plane, and their symmetrical number is grounded on the same 

 law which is so common amongst Cryptogams, even where or- 

 ganisms are derived from the contents of cells, as for example, 

 in the asci of Fungi and Lichens. Supposing the observation 

 were correct, which describes the tip of the columella as oc- 

 casionally producing leaves, this would be no confirmation of 

 the doctrine that the teeth of the peristome are of similar 

 origin, as they would be derived in a manner altogether differ- 

 ent in the two cases. 



