BOTANICAL GEOGRAPHY i ae 
(Ammophila) of the Atlantic coast and the great lakes, 
will continue to grow upward as the sand is piled about 
: them by the winds until they 
e. have risen to a level of a 
: ' hundred feet above the start- 
' ing point. 
Ae Peat bogs are especially 
;. ' characterized by the predominance of 
the peat mosses (Fig. 231) from which 
they take their name. 
These plants and the others which associ- 
ate with them are mostly hydrophytes, living 
usually with a considerable portion of the 
plant continually submerged in the bog 
water. The water of such bogs contains 
a ‘ little mineral matter and only a very scanty 
BS supply of nitrogen, in the form of nitrates 
_ dissolved in it. The bog-plants, therefore, 
“ve” must either get on with an exceptionally 
a 
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4) 
small supply of nitrogen or they must get 
i it from an unusual source. The peat mosses 
4 adopt the former alternative, while the sun 
ik. dews (Fig. 238), the pitcher-plants (Fig. 
237), and some other species adopt the latter and 
derive their nitrogen supply largely from insects — 
which they catch, kill, and digest. 
399. Arctic Vegetation. — The seed-plants of the 
Fic. 231. arctic flora are mostly perennials, never trees. 
Peat Moss. By the large bulk of the underground portion 
as compared with that of the part above ground, they 
are adapted to a climate in which they must lie dormant 
