324 BOTANICAL GAZETTE [APRIL 
Since Sphagnum is the one macroscopic plant always present in 
bogs, our attention would naturally be directed to that. Since the 
presence of Sphagnum and the lack of drainage are the two condi- 
tions necessary for the formation of bogs, it seems probable that 
in this combination is the place to seek for the production of the 
toxin. Bacteria, however, seem to be always present in bogs and 
their excretion products are to be taken into account. 
DacHNOwWSKI (5) finds reason for believing that bacteria are 
active agents in enabling peat bogs to admit certain plants and 
exclude others. As the same investigator (4) has suggested, the 
large number of chemical and biological agents present may react 
collectively with the results of decomposition. Since it has been 
found by DacHNowskI (3) that the presence of a considerable 
amount of a finely divided insoluble substance destroys the toxic 
effect of bog water, it seems possible that the absence from bogs 
of ordinary insoluble soil substances may be a factor in the produc- 
tion of toxicity in bogs. 
DACHNOWSKI (5) has given recently a historical summary of 
the theories of the causes of the xerophilous character of bog plants. 
In this summary he says ‘‘LiviNcsToNn suggests the presence of 
chemical substances not in direct relation to the acidity of the soil 
as acting on the vegetation. Another explanation, that of the 
toxicity of the habitat and its consequent physiological aridity 
and selective operation upon forms striving for occupancy, has been 
offered by the writer of this paper.’’ In the paper above quoted 
LIVINGSTON says “the result of these tests is, briefly, that many 
bog waters act upon the plant [Stigeoclonium] like poisoned solu- 
tions.”’ Again, he says ‘diluting the . . . . samples .. . . with 
distilled water or with a weak nutrient solution decreases the 
toxic effect.” In his summary he says “the stimulating substances 
here demonstrated may play an important réle in the inhibition 
from bogs of plants other than those of xerophilous habit.” 
It seems to the writer that the toxin theory of the cause of the 
exclusion from bogs of plants other than certain xerophytes origi- 
nated with Livincston. The theory has been greatly extended and 
a wealth of experimental data given to support it by DACHNOWSKI, 
