322 BOTANICAL GAZETTE [APRIL 
excluded certain plants from bogs, but did not express any opinion 
on root hairs, while CovILLeE stated the theory that certain plants 
were devoid of root hairs as a protection against bog poisons, but 
does not give an opinion whether the bog habitat as it at present 
exists caused the loss of these root hairs. Neither does he express 
any opinion as to how mesophytic plants are kept out of bogs. 
It is to be borne in mind that CoviLLE was working on a specific 
economic problem and evidently did not concern himself, in the 
paper quoted, with questions of pure science. DACHNOWSKI at 
first thought that toxins caused xerophily in bog plants and later 
that the toxicity caused bogs to exercise a selective operation, but 
does not suggest any injurious effect of bog toxins on root hairs 
as the cause of such selective operation. 
TRANSEAU’S work (10) would seem to suggest that Larix 
laricina is adapted to the Michigan bogs because it can still live 
after the loss of its root hairs and even after the destruction of the 
cortical tissues of its roots. Larix, however, is not a genus that is 
universally characteristic of bogs as are such genera as Ledum, 
Kalmia, Oxycoccus, and Vaccinium. There seems to be room fot 
doubt as to the cause of the death of the root hairs and of the cortical 
tissues of the roots of Larix in the Michigan bogs. It is possible 
that they may be killed by a toxin and attacked by a saprophytic 
fungus afterward. It is also possible that they may have been 
killed by a parasitic fungus. 
Definite conclusions as to the relation of the toxicity of the bog 
habitat as a cause and the stunting of root hairs as a result cannot, 
of course, be drawn from the results obtained from the use of water 
from six bogs on a single species. Further work must be done with 
other bog waters and other plants to show how far these two things 
are related as cause and effect. The question of how bog plants 
came to be devoid of root hairs is quite a different question from 
that as to why mesophytic plants are now excluded from undrained 
bogs. DacHNowskI, who in 1909 (3) believed in the activity of 
bog toxins in causing xerophily in bog plants, states (5) in 1911 
that “during the glacial period most species common to bogs 
skirted the ice sheet.” Whether these plants were under bog 
conditions at this time or whether their distribution was related : 
