It is very plain, from these facts, that, in forests, the mineral ingredients of the soil perform a sort of circulation; entering the root, they are deposited in the leaf; then, with it, fall to the earth, and by its decay, they are restored to the soil, again to travel their circuit. Forest soils, therefore, instead of being impoverished by the growth of trees, receive back annually the greatest proportion of those
mineral elements necessary to the tree, and besides, much organized matter received into the plant from the atmosphere; soils therefore are gaining instead of losing. If owners of parks or groves, for neatness’ sake, or to obtain leaves for other purposes, gather the annual harvest of leaves, they will, in time, take away great quantities of mineral matter, by which the soil, ultimately, will be impoverished, unless it is restored by manures.
Leaf-manure has always been held in high esteem by gardeners. But many regard it as a purely vegetable substance; whereas, it is the best mineral manure that can be applied to the soil. What are called vegetable loams (not peat soils, made up principally of decomposed roots), contain large quantities of earthy matter, being mineral-vegetable, rather than vegetable soils.
Every gardener should know, that the best manure for any plant is the decomposed leaves and substance of its own species. This fact will suggest the proper course with reference to the leaves, tops, vines, haulm, and other vegetable refuse of the garden.
The other fact connected with the leaf, is its function of Exhalation. The greatest proportion of crude sap which ascends the trunk, upon reaching the leaf, is given forth again to the atmosphere, by means of a particularly beautiful economy. The quantity of moisture produced by a plant is hardly dreamed of by those who have not specially informed themselves. The experiments of Hales have been often quoted. A sun-flower, three and a half feet high, presenting a surface of 5.616 square inches exposed to the sun, was found to perspire at the rate of twenty to thirty ounces avoirdupois every twelve hours, or seventeen times more than a man. A vine with twelve square feet exhaled at the rate of five or six ounces a day. A seedling apple-tree, with twelve square feet of foliage, lost nine ounces a day.[6]
These are experiments upon very small plants. The vast amount of surface presented by a large tree must give off immense quantities of moisture. The practical bearings of this fact of vegetable exhalation are not a few. Wet forest-lands, by being cleared of timber, become dry; and streams, fed from such sources, become almost extinct as civilization encroaches on wild woods. The excessive dampness of crowded gardens is not singular, and still less is it strange that dwellings covered with vines, whose windows are choked with shrubs, and whose roof is overhung with branches of trees, should be intolerably damp; and when the good housewife is scrubbing, scouring and brushing, and nevertheless, marvelling that her house is so infested with mold, she hardly suspects that her troubles would be more easily removed by the axe or saw, than by all her cloths and brushes. A house should never be closely surrounded with shrubs. A free circulation of air should be maintained all about it, and shade-trees so disposed as to leave large openings for the light and sun to enter. Unusual rains in any season produce so great a dampness in our residences that no one can fail to notice its effect, both on the health of the occupants, and upon the beauty and good condition of their household substance.
The following method to destroy weeds is pursued at the mint in Paris, with good effect: 10 gallons water, 20 lbs. quicklime And 2 lbs. flowers of sulphur are to be boiled in an iron vessel; after settling, the clear part is thrown off and used when needed. Care must be taken, for if it will destroy weeds it will just as certainly destroy edgings and border flowers if sprinkled on them. Weeds, thus treated, will disappear for several years.
[5] See Dr. Grey’s Botanic Text Book, an admirable work, which every horticulturist should own and study.
[6] Lindley’s Horticulture, p. 42-44. Grey’s Botany, p. 131.