Ex 
Ey a & 
PLANT SOCIETIES 201 
the peat moss must be those which give off water into 
the air slowly, since the cold water and certain acids 
about their roots in the dead peat below the surface 
prevent the roots Irom taking up water rapidly. 
The vegetation on the margin of the peat bog. On 
the margin of the peat bog, where the ground is drier 

Fic. 302. Peat moss or sphagnum. 
and contains more soil, you may see the plants drawn 
up in battle array. The societies are struggling among 
themselves, and are also pushing their way slowly out 
into the peat. The story of the advance is plainly told 
