Читать книгу: «The Mirror of Literature, Amusement, and Instruction. Volume 19, No. 529, January 14, 1832», страница 4

KNOWLEDGE FOR THE PEOPLE

(From Part xiii.—Botany.)

Why have vegetables the function of transpiration?

Because the sap, on arriving in the leaves, loses and gives out the superabundant quantity of water which it contained.

Why are limpid drops often observed hanging at the points of leaves at sunrise?

Because of the vegetable transpiration condensed by the coldness of the night. It was long thought that they were produced by dew; but Mushenbroëk first proved the above, by conclusive experiments. He intercepted all communication between a poppy and the ambient air, by covering it with a bell; and between it and the earth, by covering the vessel in which it grew with a leaden plate. Next morning the drop appeared upon it as before—Richard.

One of the hydrangea tribe perspires so freely, that the leaves wither and become crisp in a very short space of time, if the plant be not amply supplied with water: it has 160,000 apertures on every inch square of surface, on the under disk of the leaf.

Why is more or less of a gummy, resinous, or saccharine matter found in every tree?

Because it is formed by branches of those returning vessels that deposit the new alburnum.

Why is it inferred that these juices must be prepared in the plant itself, by various secretions, and changes of the fluids which it absorbs?

Because we find, that in the same climate, nay, even in the same spot of ground, rue has its bitter—sorrel its acid—and the lettuce its cooling juices; and that the juices of the various parts of one plant, or even of one fruit, are extremely different. Sir James Smith mentions the peach-tree as a familiar example. "The gum of this tree is mild and mucilaginous. The bark, leaves, and flowers, abound with a bitter secretion, of a purgative and rather dangerous quality, than which nothing can be more distinct from the gum. The fruit is replete, not only with acid, mucilage, and sugar, but with its own peculiar aromatic and highly volatile secretion, elaborated within itself, on which its fine flavour depends."—Introduction to Botany, 6th edit.

Why are these juices readily found in the bark?

Because they appear to be matured, or brought to greater perfection, in layers of wood or bark that have no longer any principal share in the circulation of the sap. Thus, the vessels containing them are often very large, as the turpentine cells of the fir tribe, in all the species of which these secretions abound. The substance from which spruce-beer is made, is an extract of the branches of the Abies Canadensis, or Hemlock Spruce; a similar preparation is obtained from the branches of Dacrydium, in the South Seas.

Why, in the spring, is the herbage under trees generally more luxuriant than it is beyond the spread of their branches?

Because the driving mists and fogs becoming condensed on the branches, cause a frequent drip beneath the tree not experienced in other places; and thus keep up a perpetual irrigation and refreshment of the soil.

Why are certain plants useful or injurious to others that grow in their vicinity?

Because of certain fluids which the roots excrete from their slender extremities; and in this manner the likings and antipathies of certain plants may be accounted for. Thus, it is well known that the creeping thistle is hurtful to oats, erigeron acre to wheat, scabiosa arvensis to flax, &c.

Why are some resins odorous?

Because they contain essential oil; some afford benzoic acid when heated, and these have been termed balsams; such as tolu balsam and benzoin.

Common resin is obtained by distilling the exudation of different species of fir; oil of turpentine passes over, and the resin remains behind.

Why are the varieties of the cashew tribe, called varnish-trees?

Because their large flowers abound in a resinous, sometimes acrid, and highly poisonous juice, which afterwards turns black, and is used for varnishing in India. One kind is the common cashew nut. All these varnishes are extremely dangerous to some constitutions; the skin, if rubbed with them, inflames, and becomes covered with pimples that are difficult to heal; the fumes have also been known to produce painful swelling and inflammation.

Why do these varnishes, at first white, afterwards turn black?

Because the recent juice is an organized substance, consisting of an immense congeries of small parts, which disperse the sun's rays in all directions, like a thin film of unmelted tallow; while the varnish which has been exposed to the air loses its organized structure, becomes homogeneous, and then transmits the sun's rays, of a rich, deep, uniform, red colour.

The leaves of some species of Schinus are so filled with a resinous fluid, that the least degree of unusual repletion of the tissue causes it to be discharged; thus, some of them fill the air with fragrance after rain; and other kinds expel their resin with such violence when immersed in water, as to have the appearance of spontaneous motion, in consequence of the recoil. Another kind is said to cause swellings in those who sleep under its shade.—Brewster's Journal.

Why is the soap-tree so called?

Because its bark, if pulverized, and shaken in water, soon yields a solution, frothing, as if it contained soap. It is a native of Chili; the trunk is straight, and of considerable height; the wood is hard, red, and never splits; and the bark is rugged, fibrous, of ash-grey colour externally, and white within.

Why is a species of myrtle called the wax-tree?

Because the leaves and stem, when bruised, and boiled in water, yield wax, which concretes on cooling. Mr. Brande observes, "the glossy varnish upon the upper surface of many trees is of a similar nature; and though there are shades of difference, these varieties of wax possess the essential properties of that formed by the bee: indeed, it was formerly supposed that bees merely collected the wax already formed by the vegetable: but Huber's experiments show, that the insect has the power of transmuting sugar into wax, and that this is in fact a secretion."

The wax-palm of Humboldt has its trunk covered by a coating of wax, which exudes from the spaces between the insertion of the leaves. It is, according to Vaquelin, a concrete, inflammable substance, consisting of 1/3 wax, and 2/3 resin.

Why are some oils called vegetable butters?

Because they become solid at the ordinary temperatures. Such are cocoa-nut oil, palm oil, and nutmeg oil.

Why are some volatile oils obtained by expression?

Because they are contained in distinct vesicles in the rind of fruits, as in the lemon, orange, and bergamot.

Why is the oil of poppy-seed perfectly wholesome?

Because it is in no degree narcotic; nor has it any of the properties of the poppy itself. This oil is consumed on the Continent in considerable quantity, and employed extensively in adulterating olive oil. Its use was at one time prohibited in France, by decrees issued in compliance with popular clamour; but it is now openly sold, the government and people having grown wiser.

Why is the juice of the poppy called opium?

Because of its derivation from the Persian afioun, and the Arabian aphium. The botanical name of the poppy, papaver, is said to be derived from its being commonly mixed with the pap, papa, given to children in order to ease pain, and procure sleep.

Why does opium produce sleep?

Because it contains an alkaline substance called Morphia. The same drug contains a peculiar acid called the Meconic; and a vegetable alkali named Narcotine, to which unpleasant stimulating properties are attributed by Majendie.

Why is sugar so generally found in plants?

Because it is not only the seasoning of most eatable fruits, but abounds in various roots, as the carrot, beet, parsnip, and in many plants of the grass, or cane kind, besides the famous sugar cane.

Sir James Smith observes that "there is great reason to suppose sugar not so properly an original secretion, as the result of a chemical change in secretions already formed, either of an acid or mucilaginous nature, or possibly a mixture of both. In ripening fruits, this change is most striking, and takes place very speedily, seeming to be greatly promoted by heat and light. By the action of frost, as Dr. Darwin observes, a different change is wrought in the mucilage of the vegetable body, and it becomes starch."

M. Berard considers gum and lignin as the principles in unripe fruits which chiefly tend to the formation of sugar during their ripening, and he has given several analyses of fruits in illustration of these views. Mr. Brande also considers the elements of water as probably concerned in the change.