Sphagnum 



349 



and runners of other stronger plants. It is the inter- 

 penetration of these that binds the bog cover together, 

 making it resilient under foot. 



The leaves of Sphagnum are interspersed with cells 

 that are mere water reservoirs having porous walls. 

 Some of these leaves are deflexed against the stem and 

 make excellent capillary 

 conduits for water upward 

 or downward. Whether the 

 abundant supply be in the 

 air above or in the soil be- 

 low, these make provision 

 for the equitable distribu- 

 tion of it. Wherefore, these 

 masses of sphagnum become 

 water reservoirs, holding 

 their supply often against 

 gravity, and bathing the 

 roots of all the cover plants 

 that rise above the surface 

 of the bog. 



Sphagnum belongs to the 

 shore, and it is quite incap- 

 able of advancing into the 

 water unassisted. But with 



the help of stronger more straggling plants whose roots 

 and branches penetrate and interlace in its masses in 

 mutual support, it is able to extend as a floating border 

 out over the surface of still water in small lakes and 

 ponds. These floating edges may be depressed by the 

 weight of a man until they are under water, but they 

 are tough and elastic, and rise again unharmed when 

 the weight is removed. Long, strong, pliant-stemmed 

 heaths and slender sedges are the plants commonly 

 associated with sphagnum in the making of this floating 

 border. In the bog cover equally close is its association 

 with the common edible cranberry. 



FIG. 206. 



a b 



Bog moss, Sphagnum; 



a the tip of a spray; b, a. few cells from 

 a leaf; x, long interlaced lines of slen- 

 der sinuous chlorophyl-bearing cells, and 

 y, large empty water reservoir cells hav- 

 ing pores in their walls for admission of 

 water and annular cuticularisations 

 for support. 



