search of moisture and soluble matters, and by an incomprehensible vital power, transfers them into the body of the plant, where they undergo mysterious elaboration to form the fluid called sap.

The terminal fibres of the radicle are so minute as almost to defy detection by the aid of a microscope, and if injured, they will not fully exert their proper functions; therefore, in transplanting, we always endeavour to avoid wounding them with the spade, by digging some distance around the stem, and thus carrying away with the plant a large ball of earth, through which the terminal fibres have not penetrated.

This precaution protects the radicle, and also the plant, from sustaining the derangement of its functions that would ensue, if it were rudely torn up, and suddenly transplanted to a soil physically and chemically different to that in which it originally germinated and grew; the plant continues to draw for food upon its parent clod of earth, until its organs are enabled to pierce beyond such limit, and to become inured to the change of nutriment presented by the neighbouring soil.

The chemist is acquainted with numerous substances which act as poisons upon the animal frame; of these, white-arsenic, corrosive-sublimate, blue-vitriol, prussic acid, and opium, may be cited as examples; and he discovers that any of these, if dissolved in water, and. applied to the roots of a plant, will soon cause it to languish, droop, and die.

Many experiments have been made upon this destruction of the vitality of plants by poisonous substances; the following are a few of the most remarkable.

Beans were watered with a solution of white-arsenic ; they faded in the course of a few hours, then became yellow, and in three days were dead.

A lilac was killed by the introduction of a portion of solid white-arsenic into a cut made in one of its branches; and a similar effect was produced by corrosive-sublimate.

Beans were killed by prussic acid in the course of a single day, and deadly nightshade in four days; while spirit of wine killed the plant to which it was applied in a few hours.

An experiment can be easily made regarding the poisonous action of a metallic solution upon a plant.

For example, water a succulent plant with a solution of blue vitriol (sulphate of copper) until it die; then cut its stem across with a perfectly clean steel knife; and that the poisonous compound has been transferred to the plant, and caused its death, will be evident by bright metallic copper appearing on the knife-blade.

All things are so miraculously adjusted throughout Nature, that the earth seldom or ever presents the roots of plants with poisonous matters, but in their stead, soluble compounds of potash and lime, which, under the influence of vitality, promote the elaboration of healthy sap or vegetable blood. The chemist can throw but very little light upon the composition of

sap, and no analysis unto which it has been subjected, can be regarded as correct, on account of the difficulty of obtaining it in a normal state, or free from other juices of the plant; the cause of its motion or circulation is also a mystery; it is observed to travel through the stem and the branches, and chiefly towards the leaves, it enters their peculiar structure as a comparatively thin fluid, containing a large amount of water ; and by the combined agencies of heat, air, and light, much of this is evaporated in a pure state, or in other words, the sap becomes thickened, .or concentrated, and excited to form new proximate principles, which increase the growth of the entire plant.

Upon close examination, the chemist discovers this evaporation to be enormous; for example, a large sunflower was proved to lose one pound four ounces, and a cabbage one pound three ounces, of water during twenty-four hours; and many plants were proved to lose one hundred times their weight of water during three months.

This evaporation of water from plants may be proved very readily, by covering them with a cold, dry, bellglass, for in the course of a few minutes its interior will become lined with small drops of water resulting from the condensation of the vapour; and that it ensues chiefly from the lower surfaces of the leaves, may be shown by placing them between two cold, dry plates of glass, as represented in the opposite sketch.

Drops of water will thus condense most abundantly

upon the glass plate, which is opposed to the lower surfaces of the leaves; "their organization is such, as to render these surfaces the most apt for the escape of watery vapour; but in some plants the upper surfaces are said to be most active."

Fig. 17.

As evaporation thus proceeds from the leaves, they incessantly demand a fresh supply of moisture from the roots; and if the soil be too dry, or water not abundantly furnished to meet the demand, the plant will inevitably sustain derangement of its functions.

Plants are frequently "blighted" during early Spring, by dry winds, for when branches and leaves are first put forth, they are extremely succulent, and part with water so readily, that during a dry easterly wind this loss by evaporation cannot be rapidly compensated for, by the capillary attraction of the roots.

The drooping of a plant during a hot day, mainly depends upon the extreme evaporation of water that has been excited from the leaves, and the inadequacy of the terminal fibres of the roots to collect more with sufficient rapidity from the arid earth; if then water be artificially added to it, the plant revives, sometimes with extraordinary quickness.

Leaves have not only the power of transpiring the vapour of water, but likewise of absorbing it under certain conditions; thus a plant, drooping beneath the heat of Summer, will soon revive if placed in a damp cellar; the leaves absorb the damp, or vapour of water, and through its genial influence the plant speedily regains its wonted strength and beauty.

The leaves in their exercise of these functions of evaporation and of absorption are of vital importance to plants; and upon stripping them away, the plants suffer in health, or suddenly die.

The further consideration of the vital functions of plants upon surrounding media, will be presented in the next Chapter; and in proportion as we extend these researches, so shall we have cause to appreciate, with admiration and gratitude, the power and goodness of the Creator.

"He causeth the grass to grow for the

cattle, and herb for the service of man: that he may bring forth food out of the earth.”