"Air, air, fresh life-blood, thin and searching air, The clear, dear breath of God that loveth us."
Air is invisible, and earth a very tangible thing indeed, which makes us forget sometimes how much air does for us, to feed and nourish. We do not only live in it, we live of it; and by we I mean all breathing creatures, whether men or lower animals or plants. What brings the truth most home to us is having to do without air - in a London fog, for instance.
We have been talking a great deal about the flowers and plants of London. Alas! very few of them are grown there; most of them have to be imported. During the winter months fog is too terrible an enemy, so insidious is it, playing havoc even with our indoor and conservatory plants.
It is interesting to learn from the researches of the savants, that the evil effect of urban fog on flowers and foliage is twofold. The injuries are produced in two quite separate ways: one is the presence of poison in the atmosphere; the other, the reduction of light, which is the invariable result of the fog of cities and manufacturing towns.
Darkness and poison! Does not this sound worse than a plague of Egypt? Yet we town-folk suffer it without much grumbling, and scientists spend as much time in learning what the poison consists of, and in tracing exactly how the injuries come about, as would suffice, one would imagine, to discover a cure. Oddly enough, more poisons are found in fog than even coal-burning altogether accounts for; the exact nature of some of the substances which are present in the atmosphere of foggy weather is a matter about which scientists themselves confess to ignorance.
Still, there is one thing on which all agree, and that is the perfect harmlessness of clean mist. Neither mountain nor country mists do any wrong to plant life, and from the coasts of Kent and Sussex, Essex and Norfolk, come assurances of the innocuous character of sea-fogs.
Of the known impurities of town-fog the following list gives most of those suspected of being inimical to plants. "Suspected" is the scientific way of putting it. Our scientists are wary; they must be, for they know how everybody weighs their words; and besides that, they can never be sure what fresh discoveries will be made tomorrow; the latest are oftentimes upsetting.
The amount of miscellaneous ingredients that enrich a London fog is startling. Our list is taken from an analysis of the deposits left on the glass roofs of plant-houses at Chelsea and Kew during the severe fogs of February, 1891: Carbon, hydrocarbons, organic bases, sulphuric acid, hydrochloric acid, ammonia, metallic iron, and magnetic oxide, with other mineral matter, chiefly silica and ferric-oxide. Sulphuric acid, it seems, is the principal cause of injury to trees and shrubs, and sulphurous acid to herbaceous and soft-wooded plants.
The effects of fog are seen sometimes in the breaking-down of the plant, sometimes in its discoloration; leaves gradually turn yellow, progressing from below upwards, and they drop off in the order in which they showed the change of colour. Thus two things have happened: destruction of the green colouring matter, and structural injury at the point where leaf meets stalk. Where is the London flower-grower who has not watched these processes with sad eyes? When an ill wind blows soot-laden fog towards Kew or Chelsea - places where so many of our choicest plants and trees and flowers are cherished - loud are the lamentations because of damage done.
Mr. Watson, assistant curator of the Royal Kew Gardens, says he gathers up bushels of leaves in the palm-houses every morning while a bad fog lasts, and after a long spell of it many hard-wooded as well as the more delicate plants are reduced to an unsightly condition of almost bare stems, blotched and discoloured leaves, and fallen foliage. Among certain groups even the soft stems disarticulate at the nodes.
Mr. W. Thiselton-Dye, Director of Kew Gardens, describes the substance deposited on his glass-houses as a solid brown paint, weighing about twenty-two pounds to the acre, or six tons to the square mile. This makes our fog enemy appear a very real thing indeed; no wonder it breaks plants down, and is the ruin of many fruit and floral industries in the south of London.
Are there any means by which town cultivators may counteract these malign influences? Only by very expensive appliances. The grower wants an air-tight greenhouse, with definite openings where the admitted air can be filtered. Filtering foggy air may counteract or even keep out poison, but even then one has to make up for the darkness. This can only be done by a generous installation of electric light.
Horticulture thus carried on is extremely interesting from a scientific point of view, but is not commercially desirable, nor could the ordinary flower-grower afford it. Fog-annihilators, and the use of chemicals in conservatories have also been tried, the latter with very scant success.
A Water Garden
Charcoal seems to be by far the best filtering medium. There is a Mr. Toope, who, in a small conservatory at his offices at Stepney, is endeavouring to cultivate a collection of orchids and other stove plants in safety by the use of charcoal filters and warmed air.
The method he uses is ingenious. Boxes containing open-work trays, upon which sticks of charcoal are loosely placed, are set upon the floor under the staging. These communicate with the exterior by means of apertures which can be opened or closed at will. The air (fog and all) is led from outside through these trays, passes the charcoal, impinges upon the hot-water pipes, and is then allowed to reach the plants. Draught is regulated by valves. Results so far are considered very encouraging, but not convincing. Mr. Toope has other things to occupy his attention, and sometimes has to trust his pets to others; if it were not for this, he thinks he would ensure a greater measure of success. It seems curious to think of plants taking to respirators, just as human beings have discarded them; but the use of charcoal does sound common-sensible. We are all familiar with the extraordinary power charcoal has of absorbing and oxidizing the products of decomposition of organic matter, and of rendering harmless the greater number of easily alterable gases and vapours.