A SUMMARY OF BOG THEORIES 319 



amounts of which are sufficient to supply the needs of the plant. 

 He found that bacterized peat after sterilization was an excellent 

 medium in which to grow nitrogen-fixing bacteria and apply 

 them to the soil. Schreiner (49, p. 583) has formulated the theory 

 that "degradation products of proteins are absorbed directly 

 by the plant from the soil and that the plant uses these units 

 for building up the complex proteins as far as it is possible to 

 do so." Skinner and Beattie (53, pp. 432 and 437) have shown 

 that wheat plants can utilize asparagin from soils. They also 

 quote other workers who have shown that asparagin is bene- 

 ficial to maize, oats, barley, radishes, and Lemna in water cul- 

 tures. It would thus seem that it is difficult to draw a hard 

 and fast line betw^een ''available" and "unavailable" nitrogen. 



m. The activities of micro-organisms. Dachnowski (17, p. 

 333) finds reason for beheving that bacteria are agents in enabUng 

 sphagnum bogs to admit certain plants and exclude others. 



n. Water-holding power of peat. Burns (1, p. 123) suggests 

 this and also quotes Davis (14) as favoring this view\ Coville 

 (13, p. 38) gives the following figures for the moisture equiva- 

 lent of the soils mentioned — Kalmia peat 142%, clay 30%, 

 loam 18%, sand 2% to 4%. 



o. The depth of the water table in summer. Biu-ns (1, p. 116) 

 finds reason for belie\dng that this is a factor and quotes Davis 

 (14) in support of this view. Dachnowski (20, p. 241) states 

 that "Variations in the position of the water table do not influ- 

 ence the (Oxycoccus-Sphagnum) association so greatly as is 

 often stated, nor do they offer an explanation of the xerophytic 

 structure of the plants." The water table certainly goes very 

 low in late summer in many Puget Sound bogs but water can 

 be readily squeezed from handfuls of sphagnum obtained only 

 a few centimeters beneath the surface. (But cf . Burns, 1 p. 116, 

 and Co\dlle 13, pp. 38 and 39.) 



J). Low surface tension of water. Blackman (3) reviewing 

 the work of Czapek and Lepeskin suggested that low surface 

 tension of the surrounding medium might cause the loss of water 

 from plant cells and thus work directly against osmosis and that 

 this might destroy the efficiency of the gromng points of roots. 



THE PLANT WORLD, VOL. 19, NO. 10, 1916 



