This section is from the book "The Gardener's Monthly And Horticulturist V23", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
The idea is quite common that the foliage of plants absorbs moisture while growing; and that the leaves cannot be kept healthy without frequent sprinkling. It rains on plants out doors, so we imitate the rain in doors. But according to the experiments of Bousingault, most leaves absorb moisture only when wilted, and never wilt when there is a normal supply at the roots. Hence I think the watering of foliage not only a useless operation but injurious. If water? could be applied without touching the leaves it would be all the better as far as health is concerned. The leaves do not need to be rained on or thrashed and turned by the wind to make them healthy. Water appears to be most injurious to leaves which transpire fastest. Some of these - and noticable in Caladium esculentum - are very glossy and grow inclined, and shed water as if oiled. If these are placed more horizontal and kept wet it soon injures them, especially in the sun, and when they get old so that the water really wets them they soon die.
The past winter a pomegranate and geranium tried a neat experiment. The pomegranate was growing rapidly and there was a small drop of water on the tip of each young leaf most of the time. One of these leaves was about one-fourth of an inch above a geranium leaf; the effect was to kill a spot one inch in diameter while the rest of the leaf remained healthy and green. Some might think the leaves of the pond-lily required the water to rest upon while growing but it is only the old leaves that lay upon the water. The young leaves grow several inches out of the water, and will grow vigorously for months without touching the water. When the old leaves get so they do not shed water they soon get drowned.
Parisitic plants which require a damp atmosphere, transpire the least of any, and really need much less water than those that root in the ground. Because they are mostly dependent upon the moisture of the atmosphere, we must not suppose they need as much water as do those which have a permanent supply at the roots and are not dependent upon the atmosphere. In traveling through the South one will see the finest specimen of "Spanish Moss" in ravines where there is a constant evaporation in the day and condensation at night.
The leaves of plants are frequently compared to the lungs of animals, but they correspond to the digestive organs rather than lungs. It is the under-side of the leaf which transpires water and waste product, and the upper side which is exposed to the direct rays of the sun that the main chemical transformations takes place. When a plant grows the sap-water must carry in solution the necessary alkalies for digesting the carbonic acids. So if we make plants grow at all by leaf absorption we must mix in the required alkalies. Would this not be about as absurd as to bathe infants continually in milk to make them grow. Again the transpiration and circulation must be continous during growth and it would not be consistent for plants to absorb water and transpire it at the same time.
During rapid growth in sun light transpiration is about five times as much as at night. This would also indicate that the growth taking place in daylight did not need a moist atmosphere, and that the heat and light of the sun and a dry atmosphere which facilitates transpiration is most essential to hardy growth. We hear much of the dry air of the living room, but what is that compared to 90° in the shade and 130° in the sun with the wind at 40 miles an hour. It is not convenient to sprinkle plants in the house, and if it assists growth I have yet to find it out. I grow (not merely keep them alive) some thirty species and never think of watering the leaves. I have leaves four years old, green and healthy, that are within eight feet of the stove.