This section is from the book "The Gardener's Monthly And Horticulturist V21", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
In the July number, Mr. Milton seems to think he has settled this question when he tells us his Bilbergias have made a growth without roots, and that when we sprinkle a lot of unrooted wilted cuttings, we know that in a short time they will regain their plumpness in leaf and stem. That this statement is correct there is no doubt, and it does seem on first view to annihilate my doubts.
On the 2d of July, the day I received the Monthly, I cut off fifty strong growing soft shoots of Geraniums, Petunias, Verbenas and Heliotropes, threw them down in the hot sun until they were thoroughly wilted. One half of them I immersed in soup plates filled with water; the cut ends of the other half I covered with soft putty and oiled paper, so as to prevent absorption through the cut stem even from the air. I then immersed all of these in*the water except the sealed ends. I placed them in a greenhouse over night, and in the morning found that those that had been completely immersed were as fresh as when cut from the living plants, while those that were immersed with the sealed up stem out of the water were limp and wilted, seemingly as much so as when immersed. Now if I am correct in this experiment, and it is easily tried, it is fair to infer that the sprinkled cuttings, resuming their plumpness as referred to by Mr. Milton, absorbed through the cut stem rather than the leaves. For if absorption had taken place through the leaves, the sealed up lot would have been as fresh as the others, for only the part sealed up was left out of the water.
But the question may be asked why does Mr. Milton's Bilbergia increase in growth and weight while suspended without roots if my Cactuses did not? I can only answer this by supposing that the vessels of the cut stem of the Bilbergia are better fitted for absorption than those of the Cactus; or it may be that some species of plants do absorb to a limited extent through the leaves. My opinions to that extent of the subject are by no means fixed, but that they do so to an extent whereby they can be fertilized or invigorated so as to give any practical assistance in their culture by being stimulated with ammonia or nitrogen applied to the leaves only, I yet very much doubt.
Mr. Milton says that the reason that vegetation in the immediate vicinity of bone factories, etc., is not improved by the exhalations therefrom is because it is not in condition to be absorbed. Why not ? If the open air is charged with ammonia in a rainy or moist day, in what way does it differ from Mr. Foust's greenhouse wherein he lets loose the ammonia from his heated shovel ? If the one case fails to fertilize vegetation certainly the other must, for we know from the unpleasant odors wafted for miles that in the immediate vicinity of such factories the air must be pregnant with the gases that go to feed plants, and that when carried down by the rains to the leaves, and no beneficial result follows, - and it certanly never does - this evidence goes far to deny the generally received opinion that plants can be fed through their leaves.
Mr. Foust's prescription would have inspired more confidence if he could have stated that the "improvement" he claims was shown from a comparative test. I have no doubt the plants and flowers in his careful hands showed well even after such an application, but is he sure without comparison that this was the result of the air being charged with ammonia? It is not an unusual practice for doctors to prescribe bread pills to their patients; may be it would be better if nothing else were ever prescribed. The patients improve and of course the pills are given the credit. Mr. Foust's ammonia, as he says, certainly does no harm; neither do the bread pills; but do either do any good ? They may, but I won't believe it until Mr. Foust can show that under exactly similar conditions of the same kinds of plants, grown in the same soil, temperature and moisture, that one greenhouse treated to the ammonia shows better results than another alongside without it. Any such trial as he describes, made without comparison, is never satisfactory and is always open to question.