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1914] GATES—X EROPHILY 477 
changes in weight which took place when leafy twigs were subjected 
to dry air and moist air under bell jars. A twig of Chamaedaphne 
which lost water at the rate of 0.026 gm. per hour per 100 sq. cm. 
of leaf surface in dry air, while under a bell jar with a dish of water 
gained at the rate of 0.010 gm. Twigs of Picea mariana and Larix 
laricina gained in weight in moist air at the rate of 0.00027 and 
0.000034; while those in dry air lost at the rate of 0.0061 and 
O.O111 gm. per hour per cc. of volume, respectively. 
These experiments demonstrate the ability of the living leaves 
of the three evergreen ericads and two conifers used to absorb water 
vapor in measurable quantities from saturated air. The amount 
_ So absorbed has increased the weight of a leafy twig by 6 per cent 
in 4.5 hours. When one considers the low position of bogs and the 
presence of heavy dew practically every night, no inconsiderable 
quantity of water may be accumulated in this way and furnish a 
part of the water for evaporation during the day and so lessen the 
demand upon the roots. 
Dead leaves of Chamaedaphne absorb considerably more (3-6 
times) than living ones. The scales which are present in abundance 
on the lower sides of the leaves no doubt take an active part in this 
absorption. Their structure is very similar to those of certain 
epiphytic orchids (Vriesia) which have been shown to be water- 
absorbing. 
This function may serve to explain the excessive abundance of 
scales produced on the leaves developing in the excessively dry 
month of June 1912 at Mud Lake, in opposition to the smaller num- 
ber on the leaves of the plants at First Sister Lake which developed 
in May before drought conditions set in. 
The lessening of the drain upon the root system, when absorp- 
tion is at best difficult, is no doubt greatly assisted by vapor 
absorption by the leaves. The prevalence of dew and frost in the 
bogs even when absent on the uplands indicates the greater humid- 
ity of the bog conditions. The actual presence of snow in contact 
with the leaves greatly aids in two ways: in checking water loss, 
and in constantly furnishing water vapor which may be absorbed. 
The effect of absence of snow protection in time of cold, dry 
weather was admirably shown in the vicinity of Ann Arbor during 
