1914] GATES—XEROPHILY 451 
under the bog several inches above that of the surrounding 
country. 
Taking into consideration the rarity of real drought conditions 
of long duration, it is evident that the root system in the bog habitat 
is able more than merely to maintain these plants within their 
normal range throughout drought conditions. The xerophytic 
adaptations of the transpiring organs, of course, materially aid by 
lessening the demand upon root absorption. 
During the winter the ground is normally frozen. On account 
of the low position of bogs, they are more subject to early and late 
freezes than the surrounding country. Although the ground may 
be frozen, the covering of snow prevents the access of very low 
temperatures to the roots. In spite of the fact that the ground is 
frozen, it is evident from the continual water loss of the above- 
ground parts that some water is being absorbed by the roots, quite 
likely the water vapor evaporated from the ice into the spaces 
which become opened around the roots soon after the freezing of 
the ground. 
At any of the temperatures at which roots were dug up (down 
to —10° C.) it did not appear that any part of the plant was frozen. 
All parts were pliable to handling. The exposure of severed parts 
of Chamaedaphne for one-half an hour to —25°C. resulted in 
freezing and loss of pliability. It was repeatedly noticed that the 
leaves which had been exposed to the severest weather of the winter, 
including a temperature of —29° C., were dry, and cracked when 
bent. Later it became evident that these leaves had been killed. 
Beyond this simple test, whose limits of accuracy are not known, 
there were no suitable means of determining in the field whether 
the plant tissue was frozen. 
CONDUCTING SYSTEM 
The conducting system in bog ericads consists of a very narrow 
ring of young xylem just outside the old wood (fig. 1). There is 
a very striking similarity in the appearance of the cross-section 
of the three ericads studied. The type of stem represented in bog 
ericads is strikingly different from that of other bog shrubs in the 
relatively smaller amount of conducting tissue and in the smaller 
