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.

An examination of the different forms of vegetation was 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, while 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.  Closer 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 examination 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.  These drops, seen on vegetation on dewy nights, are therefore not dew at all, but are 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 experiments 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 recognized.

Some experiments were made on this subject in its relation to dew.  Leaves of plants that had been seen to be wet on dewy nights were experimented on.  They were connected by means of an India-rubber tube with a head of water of about one meter, and the leaf surrounded with saturated air.  All were found to exude a watery liquid after being subjected to pressure for some hours, and a broccoli leaf got studded all along its edge with drops, and presented exactly the same appearance it did on dewy nights.  A stem of grass was also found to exude at the tips of one or two blades when pressure was applied.

The question as to whether these drops are really exuded by the plant, or are produced in some other way, is considered.  The tip of a blade of grass was put under conditions in which it could not extract moisture from the surrounding air, and, as the drop grew as rapidly under these conditions as did those on the unprotected blades, it is concluded that these drops are really exuded by the plant.  Grass was found to get “dewed” in air not quite saturated.