1914] GATES—XEROPHILY 469 
With cuttings experimented upon outdoors it took even less 
transpiration for a given amount of conduction. 
The logical conclusion substantiated by these data is that the 
ability of plants of Chamaedaphne to conduct water is at all times, 
when above —15° C. (the lowest temperature at which experiments 
were performed), greater than the necessity, and that xerophytic 
modification in any part of the plant is not a result of the lack of 
ability to conduct water. 
The occurrence of temperatures of —15° is frequent in the nat- 
ural range of these plants and no injuries are apparent. At a 
temperature lower than —25°, such as occurred during February 
1912, the drying up of the exposed leaves, twigs, and flower buds 
of Chamaedaphne is first hand evidence that at such a low tempera- 
ture the conduction in the upper part of the plant is not sufficient 
to supply the transpiration demands. 
Relation of winter to the xerophily of peat bog ericads 
Among peat bog plants, ericads, with but few exceptions, retain 
their leaves during the winter, when most other plants are leafless. 
This is usually considered a matter of heredity. The presence of 
leaves very materially increases the evaporating surface of the 
plant and thereby enhances the demand for water from the 
habitat. 
That the different ericads experimented with differed among 
themselves in their transpiring ability with their degree of protec- 
tion from excessive evaporation during the winter, and that 
Chamaedaphne, the least protected, transpires considerably more 
than the leafless shrubs and trees, indicates both the effectiveness of 
the deciduous habit as a xerophytic adaptation and the necessity of 
there being other xerophytic modifications in the case of the ericads. 
Added to this, the difficulty of absorbing water is apparent, due, 
if for no other reason, to the colder temperature of the bog soil in 
winter, and the necessity of xerophytic modification. The presence 
of so many of the usual xerophytic modifications in these peat bog 
ericads is noteworthy. The thick cuticle, dense palisade layer, 
more or less sunken stomates, hairs, scales, bloom, and waxy cover- 
ings, resin, and the upright position of the leaves are all indications 
