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of Edinburgh, Session 1885 - 86 . 
weights, one of them being placed on the ground, either on grass 
or on bare soil, and the other elevated a few inches above the 
surface. The exposed surface of the one resting on the ground, 
and in heat-communication with it, is found always to keep dry on 
dewy nights, whereas the elevated one gets dewed all over. 
The effect of wind in preventing the formation of dew is referred 
to. It is shown that, in addition to the other ways already known, 
wind hinders the formation of dew by preventing an accumulation 
of moist air near the surface of the ground. 
From an examination of the different forms of vegetation made on 
dewy nights it was soon evident that something else than radiation 
and condensation was at work to produce the varied appearances 
then seen on plants. Some kinds of plants were found to be wet, 
while others of a different kind, and growing close to them, were 
dry, and even on the same plant some branches were wet, whilst 
others were dry. The examination of the leaf of a broccoli plant 
showed better than any other that the wetting was not what we 
might expect if it were dew. The surface of the leaf was not wet 
all over, and the amount of deposit on any part had no relation to 
its exposure to radiation, or access to moist air ; but the moisture 
was collected in little drops, placed at short distances apart, along 
the very edge of the leaf. Further examination showed that the 
position of these drops had a close relation to the structure of the 
leaf ; they were all placed at the points where the veins in the leaf 
came to the outer edge, at once suggesting that these veins were the 
channels through which the liquid had been expelled. An examina- 
tion of grass revealed a similar condition of matters : the moisture 
was not equally distributed over the blade, but was in drops attached 
to the tips of some of the blades. It therefore seemed probable that 
these drops, seen on vegetation on dewy nights, were not dew at 
all, but were an effect of the vitality of the plant. 
It is pointed out that the excretion of drops of liquid by plants 
is no new discovery, as it has been long well known, and the ex- 
periments of Dr Moll on this subject are referred to; but what 
seems strange is that the relation of it to dew does not seem to 
have been recognised. 
Some experiments were therefore made on this subject in its rela- 
tion to dew. Leaves of plants that had been seen to be wet on dewy 
VOL. XIII. 2 H 
