BOG XEROPHYTES AND ACID SOILS. 143 



whether they be chlorophyllous plants, molds, bacteria, protozoa, 

 etc., but it is highly probable that bacteria and molds play the major 

 role. As a consequence, there is nothing fundamentally antagonistic 

 between the view that lack of oxygen is the chief factor in bogs, and 

 the view that toxic substances play the controlling part. Both must 

 be taken into account, but the place of first importance must be 

 accorded to lack of oxygen, since it not only affects plants pro- 

 foundly itself, but also because it bears a causal relation to the ac- 

 cumulation of carbon dioxid and other toxic substances. 



Much additional investigation is required to determine the re- 

 spective shares of the lack of oxygen alone, the accumulation of 

 carbon dioxid, the presence of organic acids, and of other toxic com- 

 pounds in the characteristic effect of bog-water. The results of 

 many researches have shown that a deficient oxygen supply inhibits 

 absorption, photosynthesis, respiration, tropistic response, and 

 growth, while amounts of carbon dioxid ranging from 2 to 20 per cent 

 produce in addition a toxic effect, which further inhibits function- 

 ing, growth, and reproduction. While the results of Hesselmann 

 and of Bergman in particular indicate that the low oxygen-content 

 and the corresponding abundance of carbon dioxid are sufficient to 

 explain the effect of bog-water, studies of root excretion under anaer- 

 obic conditions, and of the effect of the organic acids excreted, make 

 it clear that these are sometimes concerned at least. 



Wehmer (1891, 1906) has shown that the oxalic acid produced by 

 certain fungi is very toxic to plants, and Lovinson (1900 : 217) 

 has found that solutions of formates, acetates, or propionates hin- 

 dered germination, and decreased growth and functioning, as a con- 

 sequence of their effect upon the protoplasm and nucleus of the root- 

 cells. Stiehr (1903) has studied the effect of acetic, oxalic, and citric 

 acids upon root-hairs, and finds that very dilute solutions cause the 

 death of the root-tip and even the entire root. This result was 

 brought about by a solution of 0.02 per cent in the case of each acid 

 with a maximum exposure of 3 hours. 



Aso (1906) has observed that sodium or calcium acetates or for- 

 mates exert an injurious effect upon higher plants, similar to that pro- 

 duced by free acetic or formic acid. It seems certain that bogs must 

 contain other toxic organic substances, similar to those isolated by 

 Schreiner, Reed, Shorey, and others, from various soils, while the 

 work of Kaserer (1905) shows that the hydrogen and methane de- 

 rived from the anaerobic fermentation of cellulose inhibit nitrifica- 

 tion, and may affect other aerobic processes. 



