Mossworts 147 



level and rise again when the weight is removed. The 

 part of the mat which the sphagnum composes consists 

 of erect, closely-placed, unbranched stems, like those 

 shown in fig. 59, which grow ever upward at their tips, 



FIG. 59. Bog moss, Sphagnum. 



and die at the lower ends, contributing their remains 

 to the formation of beds of peat. 



The leaves of Sphagnum are composed of a single layer 

 of cells that are of two very different sorts. There are 

 numerous ordinary narrow chlorophyl-bearing cells, and, 

 lying between these, there are larger perforate reservoir 

 cells, for holding water. 



