312 GEORGE B. RIGG 



{e.g., southwestern Alaska). They may border on an open 

 lake {e.g., Mud Lake and Echo Lake, King County, Wash- 

 ington) or they may even completely surround the lake {e.g., 

 Little Crystal Lake, Snohomish County, Washington). They 

 may occur in valleys {e.g., Henry bog near Seattle) or in depres- 

 sions in the tops of considerable elevations {e.g., Monroe, Wash- 

 ington, and Mitrofania Bay, Alaska). They may also occur 

 as relatively small patches in the tundra {e.g., Yakutat, Alaska). 

 As the writer has stated before (42, p. 180) the two conditions 

 that seem to attend the formation of a sphagnum bog are a 

 considerable growth of sphagnum and the accumulation of 

 the products of its slow decay in the absence of drainage. 



THE XEROPHILY OF BOG PLANTS 



The flora of sphagnum bogs is widely recognized as being 

 prevailingly xerophytic. It is distinctly so in the bogs of the 

 Puget Sound region and of the coastal region of Alaska (Rigg 

 41, p. 314, 42, p. 181). That is, the plants characteristic of 

 these bogs show such structural characters as we would expect 

 in plants growing in dry places, in spite of the fact that the 

 substratum in which they grow is wet. This is ''physiological 

 drought" as distinguished from physical drought. 



The view that bogs are not exclusively xerophytic has been 

 advanced by Clements (7, pp. 168-170) and by Burns (1, pp. 105 

 and 124). It is evident that this apparent diffeience in opinion 

 is a mere question of the definition of terms. Clements evidently 

 uses the term "bog" in a very broad sense to include swamps 

 and ponds and not at all in the strict sense of "sphagnum bogs." 

 He pictures (p. 169) Sagittaria latifolia as a "bog plant." When 

 Burns (1, p. 124) states that "The bogs around Ann Arbor 

 (Michigan) are not xerophytic habitats, as such, but contain 

 xerophytic, hydrophytic, and even mesophytic areas," and 

 that indications are "that xerophytic conditions in bogs of south- 

 ern Michigan will shortly disappear," he is using the word "bog" 

 to include seven different successional zones the fourth one of 

 which (bog shrubs) is equivalent to the term "sphagnum bog" 



