There are two facts in the functions of the leaf, which are worth
consideration on account of their practical bearings. The food of
plants is, for the most part, taken in solution, through its roots.
Various minerals—silex, lime, alumen, magnesia, potassa—are passed
into the tree in a dissolved state. The sap passes to the leaf, the
superfluous water is given off, _but not the substances which it held
in solution_. These, in part, are distributed through the plant, and,
in part, remain as a _deposit in the cells of the leaf_. Gradually the
leaf chokes up, its functions are impeded, and finally entirely
stopped. When the leaf drops, it contains a large _per cent._ of
mineral matter. An autumnal or old leaf yields, upon analysis, a very
much larger proportion of earthy matter than a vernal leaf, which,
being yet young, has not received within its cells any considerable
deposit. It will be found also, that the leaves contain a very much
higher _per cent._ of mineral matter, than _the wood of the trunk_.
The dried leaves of the elm contain more than eleven _per cent._ of
ashes (earthy matter), while the wood contains less than two _per
cent._; those of the willow, more than eight _per cent._, while the
wood has only 0.45; those of beech 6.69, the wood only 0.36; those of
the (European) oak 4.05, the wood only 0.21; those of the pitch-pine
3.15, the wood only 0.25 _per cent._[5]
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.