Part 42

"On the 25th of May, 1768," he says, "Fahrenheit's thermometer 70°, I boiled a potato in the New-River water, till it was reduced to a mealy consistence: I put part of it, with an equal proportion of the boiling liquor, into a cylindrical glass vessel, that held something less than half a wine pint, and immediately covered it close with a glass cover. At the same time I sliced an unboiled potato, and, as near as I could judge, put the same quantity into a glass vessel of the same kind, with the same proportion of New-River water, not boiled; and, covering it with a glass cover, placed both vessels together. On the 26th of May, twenty-four hours afterwards, I examined a small drop of each by the first magnifier of Wilson's microscope, whose focal distance is reckoned 1/50th part of an inch; and, to my amazement, they were both full of animalcules, of a linear shape, very distinguishable, moving to and fro with great celerity, so that there appeared to be more particles of animal than vegetable life in each drop. This experiment I have repeatedly tried, and always found it to succeed in proportion to the heat of the circumambient air; so that even in winter, if the liquors are kept properly warm for two or three days, the experiment will succeed. I procured hemp-seed from different seedsmen, in different parts of the town; some of it I put into the New-River water, some into distilled water, and some into very hard pump-water: the result was, that in proportion to the heat of the weather, or warmth in which they were kept, there was an appearance of millions of minute animalcules in all the infusions; and, some time after, oval ones made their appearance, much larger than the first, which still continued; these wriggled to and fro in an undulatory motion, turning themselves round very quick all the time they moved forwards."

THE CHEESE-MITE.--This minute creature is a favourite subject for microscopic observations. It is covered with hairs or bristles, which resemble in their structure the awns of barley, being barbed on each side with numerous sharp-pointed processes. The mite is oviparous: from the eggs proceed the young animals, resembling the parents in all respects, except in the number of legs, which at first amount only to six, the pair from the head not making their appearance till after casting their first skin. The eggs, in warm weather, hatch in about a week, and the young animal may be seen sometimes for a day together struggling to get rid of its egg-shell. The mite is a very voracious animal, feasting equally upon animal and vegetable substances. It is also extremely tenacious of life: for, upon the authority of Leuwenhoek, though highly discreditable to his sense of humanity, we are assured that a mite lived eleven weeks after he had glued it to a pin, in order to make his observations.

We shall close the account of the curiosities of insects with a description of THE HYDRA, or POLYPES.--In natural history, this is a genus of the _Vermes Zoophyta_ class and order; an animal fixing itself by the base; linear, gelatinous, naked, contractile, and furnished with setaceous tentaculæ, or feelers; inhabiting fresh waters, and producing its deciduous offspring, or eggs, from the sides. There are five species, _H. gelatinosa_, minute and gelatinous, milk-white, cylindrical, with twelve tentaculæ shorter than the body: it inhabits Denmark, in clusters on the under side of Fuci. But on the viridis, the fusca, and the grisca, the greatest number of experiments have been made by naturalists, to ascertain their true nature and very wonderful habits. They are generally found in ditches. Whoever has carefully examined these, when the sun is very powerful, will find many little transparent lumps of the appearance of jelly, the size of a pea, and flatted upon one side. The same kind of substances are likewise to be met with on the under side of the leaves of plants that grow in such places. These are the polypes in a quiescent state, and apparently inanimate. They are generally fixed by one end to some solid substance, with a large opening, which is the mouth; the other having several arms fixed round it, projecting as rays from the centre. They are slender, pellucid, and capable of contracting themselves into a very small compass, or of extending to a considerable length. The arms are capable of the same contraction and expansion as the body, and with these they lay hold of minute worms and insects, bringing them to the mouth, and swallowing them. The indigestible parts are again thrown out by the mouth.

The green polype was that first discovered by M. Trembley: and the first appearances of spontaneous motion were perceived in its arms, which it can contract, expand, and twist about in various directions. On the first appearance of danger, they contract to such a degree, that they seem little longer than a grain of sand, of a fine green colour, the arms disappearing entirely. Soon afterwards, he found the grisca, and afterwards the fusca. The bodies of the viridis and grisca diminish almost insensibly from the anterior to the posterior extremity; but the fusca is for the most part of an equal size, for two-thirds of its length, from the anterior to the posterior extremities, from which it becomes abruptly smaller, and then continues of a regular size to the end. These three kinds have at least six, and at most twelve or thirteen arms. They can contract themselves till their bodies do not exceed one-fourth of an inch in length, and they can stop at any intermediate degree of expansion or contraction. They are of various sizes, from an inch to an inch and a half long. Their arms are seldom longer than their bodies, though some have them an inch, and some even eight inches long. The thickness of their bodies decreases as they extend themselves, and _vice versâ_; and they may be made to contract themselves, either by agitating the water in which they are contained, or by touching the animals themselves. When taken out of the water, they all contract so much, that they appear only like a little lump of jelly. They can contract or expand one arm, or any number of arms, independently of the rest; and they can likewise bend their bodies or arms in all possible directions. They can also dilate or contract their bodies in various places, and sometimes appear thick set with folds, which, when carelessly viewed, appear like rings. Their progressive motion is performed by that power which they have of contracting and dilating their bodies. When about to move, they bend down their heads and arms; lay hold by means of them, or some other substance to which they design to fasten themselves; then they loosen their tail, and draw it towards the head; then either fix it in that place, or stretching forward their head as before, repeat the same operation. They ascend or descend at pleasure in this manner upon aquatic plants, or upon the sides of the vessel in which they are kept; they sometimes hang by the tail from the surface of the water, or sometimes by one of their arms; and they can walk with ease upon the surface of the water. On examining the tail with a microscope, a small part of it will be found to be dry above the surface of the water, and, as it were, in a little concave space, of which the tail forms the bottom; so that it seems to be suspended on the surface of the water, on the same principle that a small pin or needle is made to swim. When a polype, therefore, means to pass from the sides of the glass to the surface of the water, it has only to put that part out of the water by which it is supported, and to give it time to dry, which it always does upon these occasions; and they attach themselves so firmly by the tail to aquatic plants, stones, &c. that they cannot be easily disengaged: they often further strengthen these attachments by means of one or two of their arms, which serve as a kind of anchors for fixing them to the adjacent substances.

The fusca has the longest arms, and makes use of the most curious manoeuvres to seize its prey. They are best viewed in a glass seven or eight inches deep, when their arms commonly hang down to the bottom. When this or any other kind is hungry, it spreads its arms in a kind of circle to a considerable extent, inclosing in this, as in a net, every insect which has the misfortune to come within the circumference. While the animal is contracted by seizing its prey, the arms are observed to swell like the muscles of the human body when in action. Though no appearance of eyes can be observed in the polype, they certainly have some knowledge of the approach of their prey, and shew the greatest attention to it as soon as it comes near them. It seizes a worm the moment it is touched by one of the arms, and in conveying it to the mouth, it frequently twists the arm into a spiral line like a corkscrew, by which means the insect is brought to the mouth in a much shorter time than otherwise it would be; and so soon are the insects on which the polypes feed killed by them, that M. Fontana thinks they must contain the most powerful kind of poison; for the lips scarcely touch the animal, when it expires, though there cannot be any wound perceived on it when dead. The worm, when swallowed, appears sometimes single, sometimes double, according to circumstances. When full, the polype contracts itself, hangs down as in a kind of stupor, but extends again in proportion as the food is digested, and the excrementitious part is discharged.

The manner in which the polypes propagate, is most perceptible in the grisca and fusca, as being considerably larger than the viridis. If we examine one of them in summer, when the animals are most active, and prepared for propagation, some small tubercles will be found proceeding from its sides, which constantly increase in bulk, until at last, in two or three days, they assume the figure of small polypes. When they first begin to shoot, the excrescence becomes pointed, assuming a conical figure and deeper colour than the rest of the body. In a short time it becomes truncated, and then cylindrical, after which the arms begin to shoot from the anterior end. The tail adheres to the body of the parent animal, but gradually grows smaller, until at last it hangs only by a point, and is then ready to be separated. When this is the case, both the mother and young ones fix themselves to the sides of the glass, and are separated from each other by a sudden jerk. The time requisite for the formation of the young ones is very different, according to the warmth of the weather, and the nature of the food eaten by the mother. Sometimes they are fully formed, and ready to drop off, in twenty-four hours; in other cases, when the weather is cold, fifteen days have been requisite for bringing them to perfection. The polypes produce young ones indiscriminately from all parts of their bodies, and five or six young ones have frequently been produced at once; nay, M. Trembley has observed nine or ten produced at the same time.

When a polype is cut transversely, or longitudinally, into two or three parts, each part in a short time becomes a perfect animal; and so great is this prolific power, that a new animal will be produced, even from a small portion of the skin of the old one. If the young ones be mutilated while they grow upon the parent, the parts so cut off will be re-produced; and the same property belongs to the parent. A truncated portion will send forth young ones before it has acquired a new head and tail of its own, and sometimes the head of the young one supplies the place of that which should have grown out of the old one. If we slit a polype longitudinally through the head to the middle of the body, we shall have one formed with two heads; and by again slitting these in the same manner, we may form one with as many heads as we please. A still more surprising property of these animals is, that they may be grafted together. If the truncated portions of a polype be placed end to end, and gently pushed together, they will unite into a single one. The two portions are first joined together by a slender neck, which gradually fills up and disappears, the food passing from one part into the other; and thus we may form polypes, not only from different portions of the same animal, but from those of different animals. We may fix the head of one to the body of another, and the compound animal will grow, eat, and multiply, as if it had never been divided. By pushing the body of one into the mouth of another, so far that their heads may be brought into contact, and kept in that situation for some time, they will at last unite into one animal, only having double the usual number of arms. The hydra fusca may be turned inside out like a glove, at the same time that it continues to eat and live as before. The lining of the stomach now forms the outer skin, and the former epidermis constitutes the lining of the stomach.

CHAP. XXXIII.

CURIOSITIES RESPECTING VEGETABLES.

_Curiosities in the Vegetable Kingdom--Germination of Seeds--Dissemination of Plants--Number of Plants upon the Earth--Sensibility of Plants--The Sensitive Plant._

Your contemplation further yet pursue; The wondrous world of vegetables view! See various trees their various fruits produce, Some for delightful taste, and some for use. See sprouting plants enrich the plain and wood, For physic some, and some design'd for food. See fragrant flow'rs, with different colours dy'd, On smiling meads unfold their gaudy pride. _Blackmore._

CURIOSITIES IN THE VEGETABLE KINGDOM.

The difference between animals and vegetables is so great, that at first we do not perceive any resemblance between them. Some animals only live in water; others on the earth, or in the air; and some are amphibious, or live equally well in water as upon land. And this is literally the case with vegetables: some of them only grow upon land, others in the water; some can scarcely bear any moisture, others live either in earth or water; and some even are found that exist in the air.

There is a tree in the island of Japan, which, contrary to the nature of all others, to which moisture is necessary, cannot bear the least portion. As soon as it is watered it perishes: the only way to preserve it in such a case, is to cut it off by the root, which is to be dried in the sun, and afterwards planted in a dry and sandy soil. A peculiar species of mushroom, some mosses, and other small plants, float in the air; but what is still more extraordinary, a branch of rosemary, which, as is the custom of some countries, was put in the hand of a corpse, sprouted out to the right and left so vigorously, that after a lapse of some years, the grave being opened, the face of the defunct was overshadowed with rosemary leaves. The vegetation of the truffle is still more singular: this extraordinary tubercle has neither roots, stem, leaves, flowers, nor seeds; it derives its nourishment through the pores of its bark. But it may be asked, how is it produced? why is there commonly no kind of herb in the places where this species of fungus grows? and why is the land there dry and full of crevices? These things have never been explained. No plant so much resembles animals, as that species of membranous moss called nostoch; it is an irregular substance, of a pale green colour, and somewhat transparent; it trembles upon the slightest touch, and easily breaks. It can only be seen after rain, and is then found in many places, particularly in uncultivated soils and sandy roads. It exists in all seasons, even in winter; but is never so abundant as after rain in summer. The most remarkable circumstance about it is, its speedy growth, being formed almost instantaneously: sometimes walking in the garden in summer, not a trace of it is seen, when a sudden shower of rain falling, if the same place is visited in an hour, the walks are entirely covered with it. The nostoch was long supposed to have descended from the sky; but it is now known to be a leaf, which attracts and imbibes water with great avidity. This leaf, to which no root appears to belong, is in its natural state when impregnated with water; but a strong wind or great heat soon dissipating the water, the leaf contracts, and loses its colour and transparency: hence it appears to grow so suddenly, and to be so miraculously produced by a shower of rain; for when the rain falls upon it in its dried and imperceptible state, it becomes reanimated, and appears a fresh production.

We might readily enumerate a variety of plants that bear a resemblance to animals; but there are other peculiarities in vegetables, which solicit our attention. The whole atmosphere is pregnant with plants and invisible seeds, and even the largest grains are dispersed by the wind over the earth; and as soon as they are transported to the places where they may germinate, they become plants, and often so little soil is necessary for this purpose, that we can scarcely conceive whence they derive the necessary degree of nourishment. There are plants, and even trees, which take root and grow in the clefts of rocks, without any soil. Vegetation is sometimes very rapid; of which we have instances in mushrooms, and the common cresses, the seed of which, if put into a wet cloth, will be fit for a salad in twenty-four hours. There are plants that exist with scarcely any perceptible vitality. We often see willows, which are not only hollowed and decayed within, but their external bark is so much injured that very little of it remains; yet from these seemingly sapless trunks, buds sprout in the spring, and they are crowned with leaves and branches. How admirable, that plants should not only imbibe nutriment by their roots, but that their leaves also should assist in this important function, by inspiring air! and an inverted tree will flourish as well as when in its proper position, for the branches will grow in the earth and become roots! The advanced age that some trees attain, is also very wonderful. Some apple-trees are above a thousand years old; and if we calculate the amount of the annual produce of such a tree for the above space of time, we shall find that a single pippin might supply all Europe with trees and fruit.

THE GERMINATION OF SEEDS.--Seeds are composed of different parts, according to the variety of species, the principal of which parts is the germ. Each germ has two parts: the one simple, which becomes the root; and the other laminated, which becomes the stem of the plant. The substance of most seeds is composed of two pieces, called lobes, which contain a farinaceous matter, and serve as seminal leaves to the plants. Mosses have the most simple seed, consisting only of the germ, without pellicle, and without lobes. To make seeds germinate, air, and a certain degree of heat and moisture, are necessary. The augmented heat, and the difference observable in the taste and smell, seem to denote a degree of fermentation; and the farinaceous substance becomes fitted to nourish the tender germ. It has been ascertained by experiments made with coloured fluids, that this substance imbibes a moisture, which, in conjunction with the air and heat, forms a proper nourishment till the plant has acquired strength enough to make use of the juices furnished by the root. The lobes, exhausted of their farinaceous matter, gradually dry, and fall off of themselves in a few weeks, when the plant has no further need of their assistance.--Certain herbs which grow on the mountains are of a very peculiar nature: their duration being very short, it often happens that the seed has not time to ripen; and, that the species may not be lost, the bud which contains the germ is formed upon the top of the plant, puts forth leaves, falls, and takes root. When the delicate plant shoots up from the earth, it would run too great a risk, if it were immediately exposed to the air, and to the influence of the sun. Its parts therefore remain folded close to each other, nearly the same as when in the seed. But as the root grows strong and branches out, it furnishes the superior vessels with an abundance of juice, by means of which all the organs are developed. At first the plant is nearly gelatinous; but it soon acquires more firmness, and continually increases in size.

This short account of the germination of seeds may suffice to shew, to the inquisitive in the wonders of nature, what preparations and means nature uses to produce a single plant. When, therefore, we see a seed that we have placed in the earth sprout, we shall no longer consider it as beneath our notice, but shall rather be disposed to regard it as one of those wonders of nature which have excited the observation and attention of some of the greatest of men.

Go, mark the matchless workings of that Power That shuts within the seed the future flower; Bids these in elegance of form excel; In colour these, and those delight the smell Sends nature forth, the daughter of the skies, To dance on earth, and charm all human eyes. _Cowper._

DISSEMINATION OF PLANTS.--When seeds are come to maturity, their dissemination is absolutely necessary, since without it no future crop would follow. The great Author of nature has wisely provided for this in various ways. The stems of many plants are long and slender, and being raised above the ground, the wind shakes them to and fro, and by this means are the ripe seeds conveyed to a distance. The seed-vessels of most plants are shut till the seeds are ripe, that so the winds may not scatter them prematurely; and when the proper season arrives, many of these open with such a degree of elasticity as to throw the seeds to a considerable distance. Other seeds have a kind of wings given them, by which they are conveyed to a distance of some miles from the parent plant. These wings consist either of a down, as in most of the composite-flowered plants, or of a membrane, as in the birch, alder, ash, elm, &c. Hence woods, which happen to be destroyed by fire, or any other accident, are soon restored again by new plants.

Some seeds are rough, or provided with a sort of hooks, by means of which they are apt to stick to animals that pass by them, and by this means are carried to the mouths of their burrows, where they meet with proper soil and manure for their growth. Berries and other pericarpies are by nature allotted for aliment to animals; but it is on condition that they shall sow the seed while they eat it: this they do by dispersing the seeds as they are eating; and also after eating, by voiding many of them unhurt, and even in a better state for vegetation than they were before. Thus many kinds of nuts are sown; and thus did the doves of the Moluccas replant with nutmegs those islands of the East, which the sordid avarice of the Dutch had destroyed: Providence thereby frustrating, by feeble but certain means, the contemptible selfishness of that commercial people.