180 HOFMEISTER, ON 



enveloping layer found in the interior of the upper conical 

 part of the capsule, within and beneath the layers which 

 afterwards fall off in the form of the operculum. The 

 thickening of the cell-membranes always occurs on both 

 sides. When a thickening takes place in the outer wall 

 of a cell which is occupied in forming the peristome, then 

 a portion, exactly corresponding in extent and form, of 

 the inner wall of the cell adjoining it on the outside becomes 

 thickened. When the thickened portion of the peri- 

 stome-cell is found on the wall which is directed towards 

 the axis of the capsule, then the corresponding portion of 

 the outer wall of the neighbouring cell adjoining it on 

 the inside, is thickened in like manner. These thick- 

 enings have usually the form of longitudinal stripes, and 

 are so arranged in each of the cells which help to form the 

 peristome, that they look like direct prolongations of the 

 stripes of the wall of the cell next below. When the 

 thickenings of the peristome-cells fill up the adjacent angles 

 of two laterally adjoining peristome-cells which are bounded 

 on the outside or on the inside by a cell of double width, 

 then the thickening of the wall in this wide cell occurs in 

 the form of a median stripe, which has the width of the 

 two corner stripes of the smaller neighbouring peristome- 

 cells. In the formation of the teeth of a moss with a single 

 peristome the outwardly-directed walls only of the peris- 

 tome-cells (and the corresponding mural stripes of the cells 

 adjoining on the outside) are partially thickened. In 

 mosses with double peristomes the inwardly-directed walls 

 of the peristome-cells are also thickened. When the cap- 

 sule becomes mature, the cell-walls which have remained 

 unthickened become torn during the separation of the 

 operculum from the capsule, and the thickened longitudinal 

 stripes remain as the peristome teeth. In Splaclmum and 

 Polytrichium the peristome-cells are thickened on all sides ; 

 in Splaclmum however the thickenings are irregular, those 

 which are directed outwards being much the strongest. 



Some interesting observations of Bruchs have very lately 

 been published. Gumbel's observations have shown the 

 occurrence of abnormal fruitin mosses ('Nova Acta,' vol. xxiv, 

 p. 652). Those portions of the latter observations which 



