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. 



