Plate I.—Pagoda Fig of India (Ficus religiosa).

form around the parent stem thousands of columns, which extend their ramifications, each throwing out new lateral branches and new adventitious roots. The natives love to build their temples in the intervals left between these roots of the wild fig, which, when they penetrate the soil, resume the functions of true roots. The famous Banyan-tree on the Nerbuddah is said, by the late Professor Forbes, to have 300 large and 3,000 smaller roots—aerial roots, as they are sometimes called. It is capable of sheltering 3,000 men, and thus forms one of the marvels of the vegetable world. It is, in short, a forest within a forest. (Plate I.) This is the celebrated Banyan-tree whose seeds are said to be so cooling and alterative.

Fig, 14.—Ventitious roots of the Ivy.

The stem of the Ivy (Hedera helix) is furnished with root-like processes or suckers, which seem to have no other function than that of apna supporting the plant (Fig. 14). By insinu-

THE VEGETABLE WORLD.

ating their spurs into the bark of trees or on the surface of a wall, they support the plant, but without nourishing it.*

There is one family of plants, the Cuscutaceæ, which are, above all others, parasitic. They will grow on almost any plant they can lay hold of, producing in the autumn abundance of sweet-scented flowers, but the plants to which they have attached themselves find their sap resistlessly drawn from them. The Dodder (Cuscuta Europæa), Fig. 15, is an example where the suckers form true nourishing roots.

Fig. 15.—Suckers of the Dodder plant.

The fundamental property of roots is in a physiological point of view, is their constant endeavour to bury themselves in the earth. They seem to shun the light of day, and this tendency is to be remarked from the very first moment of the root showing itself in the germinating seed. It is a tendency so decided and appears so inherent in the life of all vegetables, that if we try to go contrary to it—if, for example, we reverse a germinating seed, placing it with the root upwards—the root and the stem will twist round of themselves; the stem will stretch upwards, and the root will bury itself in the ground.

We can convince ourselves, by a very simple experiment, of the natural inclination which stems have to seek the light of day, and

This assertion may be doubted; it is no unusual thing to plant ivy on a damp wall, and the invariable result is to dry up the moisture. Who has not seen, with regret, some noble ash-tree covered with ivy, in whose embrace it is rapidly yielding up its life? Surely in those instances each adventitious root is draining the stem or walls to which it is attached of its sap, and transferring it to its own veins.—ED.

which roots have to avoid it. In a room lighted by.a single window, place a few germinating mustard seeds on a piece of cotton, and let it float on water in a vessel. It will soon be seen that the small roots point towards the dark part of the room, while the stalklets bend over to meet the rays of light coming from the window. What can be the cause which determines this natural and invincible tendency of roots towards the interior of the earth? Is it that they would avoid the light because its action might be injurious to them? Do they seek for moisture? The two following-experiments will assist the reader to answer these questions.

Place a few seeds upon a wet sponge contained in a glass tube, and light the apparatus from below. When the plant shall have germinated, and pushed out roots and rootlets, they will appear as represented in Fig. 16; the small fibres descend towards the lower part of the tube, and consequently towards the light, in obedience to

towards the light that they take their course. Take a box whose bottom is pierced with holes, as represented in Fig. 17, and fill it with mould; place a few kidney beans in these § holes, and suspend the appa- imine. el ratus in the open air. The ae ee ees roots will not ascend in order to seek the humid earth. Obedient to the inflexible law which guides them, they will be found to

descend through the holes in the box into the dry air, in which — they will soon be dried up. It is not moisture therefore that roots seek after. It has been suggested that the action of gravitation would take

Fig. 17.—Box experiment.

some part in the guidance of the roots. This is, in fact, the apparent tendency of the following experiments.

Beans have been made to germinate when placed on the circumference of an iron or wooden wheel surrounded with moss, so as to maintain the moisture of the seeds, and holding little troughs full of mould, open on two sides (Fig. 18); the wheel being put in motion in a vertical direction by a current of water and made to describe many revolutions in a minute. In consequence of this rotary movement, producing the particular force known in mechanics as centrifugal force, the action of gravitation being as it were anni-hilated, and the sprouting seed removed from its influence, and subjected to centrifugal force only; now see what occurs. The small rootlets, which in ordinary circumstances would be directed upwards, that is to say, in a direction inverse to the action of gravitation,

now turn themselves in the direction inverse to centrifugal force, or towards the centre of the wheel. The rootlets, which, under ordinary circumstances, would bury themselves in the earth, and in the direction required by the laws of gravitation, in reality now point in the direction of the force which has taken the place of gravitation. This curious experiment, carried out for the first time by Mr. J. A. Knight, a former president of the Royal Horticultural Society, has been repeated and modified in France by the ingenious naturalist, Dutr ochet. He Fig. 18.—Knight’s Vertical Wheel experiment.

Fig. 19.—Knight’s Wheel turning horizontally. seed; but as this seed is exposed at the same time to the action of centrifugal force, produced by the movement of the wheel, the c

Fig. 18.—Knight's Vertical Wheel experiment.

rootlets follow an intermediate direction between a vertical one,, which would be determined by the power of gravitation, and a horizontal one, resulting from centrifugal force. As the movement communicated to the wheel is increased in rapidity, the angle made by the root with the plane of the wheel becomes more acute also. When in a line with the wheel, the root is horizontal, and its direction outside the wheel.

The influence of gravitation in directing the course of the root is put beyond doubt by these curious experiments.

It must, however, be acknowledged that all is not mechanical in this tendency of roots to bury themselves in the earth. There exists beyond any doubt a real organic faculty belonging to the living plant.

If we compare a transverse section of the stem, with one cut from the root of one of our forest trees, the difference between the two parts of the vegetable amounts to very little. The exterior of the root is covered with a bark, very similar to that on the trunk of the tree, only the parenchyma, or cellular tissue, is never green in roots. The interior is a woody cylinder, composed of fibres, vessels, and medullary rays. Wood, therefore, forms the central portion of the root, which is almost always unprovided with the kind of vessel known by the name of duct, or trache@.* It is chiefly in this last particular that the root varies from the stem as regards its structure. When considering the stem in the next chapter, we shall get to understand these woody fibres and medullary rays. Roots ‘increase their growth at their extremities only. These extremities are always fresh, and always furnished with porous naeeepeeRAtieoaksaseeSSPSCeaPenn5moe and soft cellular tissues, the fidrilla, and their terminal point the spongiala, whose function is the absorption of the liquids or gases which are destined to penetrate into the interior of the vegetable. SORATEyoyVirctsehReeReSeatOETOMGouRdeMeTealOldeaerAE,esSoTRaeeesceERNSOmsank8EpaaeSEESeleewahkaedSea This absorption is facilitated and increased by means of the fine elongated hair-like fibres attached to all roots. Fig. 20 represents the terminal part of a root, as seen in the microscope. The true seat of absorption is not situate, as one might suppose, at the

One of the many striking analogies which exist in the structure of animals and vegetables. The trachex of insects very closely resembles the vegetable spiral duct.

aSweat-ei

aaezaeoneneensidauaePitSeontichichteaathiISeteBgSaeeA

extremity of the radicle, that is to say, at the points, but rather at a certain distance from the end, in the part marked in the engraving by the letter o.

The material which these organs take up from the soil in order to pass them into its system must either be gaseous or liquid. Solid bodies however attenuated, or however subdivided, even when held in suspension in water, cannot penetrate into the infinitely narrow channels which the extremities of the root-fibres present. All substances so absorbed must therefore be in a state of chemical dissolution in the water.

Fig. 20.—Vertical section of the extremity of a root, seen in the microscope.

The more important of these substances for the purposes of vegetation are the salts of potassium, of soda, of lime, ammoniacal compounds, and carbonic acid gas dissolved in water.

But what is the mysterious power which produces the operation of absorption in plants, this operation by which a liquid from the exterior enters and traverses an organ already gorged with liquids? Botanists have now agreed that this result is due to the triple influence, to ‘the successive or combined action of endosmose of capillary attraction and a determinate attraction in the leaves. Let us explain ourselves.

Take a small vessel, a, Fig. 21, formed of animal or vegetable membrane, containing sugared or gummed water, and plunge this vessel into another containing pure water. The liquid gum contained in the small vessel will be heavier than the pure water which surrounds it. This unequal density creates immediately a double current across the walls of the vessel;the pure water flows towards the denser gum water, while the other flows in the opposite direc-c2

Fig. 20,—Vertical section of the extremity of a root, seen roscope. in the microscope.

tion, the least dense liquid passing, however, more rapidly than the other; and if we adapt a vertical tube to the vessel, B, we see it gradually rising in the tube. This curious result is called Endosmose by chemists. This phenomenon, which has been carefully studied by chemists and botanists, is visibly in action in the vital functions of plants. The fibrous extremities of vegetables are filled with liquids and saccharine matter heavier than the water which sur-passage of water through the thin cellular exterior tissues takes place; thence the water rises up through the interior vessels of the plant, as we have seen it rise | in the tube of the Endosmometer. In this manner the first movement of ascension is produced. But the mere power of endosmose would not force the foreign fluids very far up into the vessels of the plant. A second force . which here intervenes sin- a . iANTL a gularly accelerates their Vis: SL 2 tibet upward progress. When a liquid “has begun to penetrate, by means of endosmose, at the extremities of the root, the density of the liquid contained in these radicular extremities being thus diminished by dilution, there is a current formed for them in the interior of the root. After that the force known in physics by the name of capillarity promotes the ascent of the liquid in the more elevated part of the root. The internal walls of each cell of the root exercise on the liquid which it contains the force of capillarity; in other words, an

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