Sr 
1906] TRANSEAU—BOGS OF THE HURON RIVER VALLEY 21 
and distorted, resin bodies throughout cortex and meristematic 
tissues of the wood. 
To summarize these characteristics, it is evident (1) that epidermal 
and hypodermal tissues are thick-walled; (2) that for the ccnserva- 
tion of water these are reinforced outwardly by a heavy cuticle, by 
coverings of wax and air containing hairs; (3) that resinous bodies are 
found in the roots and leaves of many of the plants; (4) that there 
is a general reduction in the size of the leaves, and that these are 
frequently revolute-margined; (5) that palisade tissue is quite uni- 
formly developed; (6) that mycorhizal fungi are present in the 
roots of most of the plants; (7) that, when compared with the xero- 
phytes of dry sand plains (25, 6), they show a similarity in respect 
to the reduction in size of the foliage, in the development of external 
protective coverings of the sub-aerial parts, and in the presence of 
palisade tissues, but are very different in the matter of root develop- 
ment and character of root structures. 
To account for the peculiarities of the bog vegetation various 
theories have been brought forward. KraiMman (28), in accounting 
for the xerophilous character of the plants of arctic swamps, which 
include several species common to American bogs, lays stress upon 
two factors: (1) the low temperature of the .moist substratum, and 
(2) the presence of drying winds. The former influences the plants 
by decreasing the power of absorption, the latter increases the rate 
of transpiration. The plants of such habitats must therefore be 
protected against the loss of water by the subaerial parts. 
SCHIMPER (44, p. 11) in classifying the natural habitats in which 
xerophytes occur mentions among others “peat, bogs, because of the 
humous acids in the soil.” On page 18 he says: _ 
The xerophilous character of the vegetation of peat moors has hitherto been 
considered an incomprehensible anomaly, and yet the rich supply of humous 
acids in the soil furnishes a condition for its occurrence as cornprehensible as it 
is necessary. The presence of Scotch pine-and heather on both dry sand and on 
Wet peat is thus not more remarkable. than is that of Ledum palustre, Vaccinium 
uliginosum, and other peat-plants on the cold dry soil in the polar zones. 
Further (p. 124) the statement occurs that ‘‘on the very acid humus 
of moors the vegetation assumes a decidedly. xerophilous character, 
because . the. humous,.acids impede the. absorption of water by the 
