THIS

WHAT ARE ANIMALS AND PLANTS?

HIS question: What are animals and plants?' is a large question. In order to be able to reply to it, we must know both (1) what animals and plants are, as contrasted with substances which are neither the one nor the other; and (2) how animals and plants stand towards each other their relations and their differences. Only by learning these two things can we possibly know what animals and plants are.

The common-sense, however, of the overwhelming majority of men will make short work of the first question; they will say: Animals and plants are living things, while all other visible substances are but composed of dead matter.' Now, we have no quarrel with common-sense, we fully accept its dictates; but the patient and admirable researches of generations of men of science, and the speculations of modern philosophers, have made known so many curious phenomena, and have brought forward so many objections, that it is no longer possible for him who would be able to give an account of the belief that is in him concerning the world and its inhabitants, to rest satisfied with such a rough-and-ready reply.

Similarly, with regard to the second question-the relations between animals and plants-most men would, perhaps, reply that animals are living creatures, which move about, and get their living by the help of their senses, while plants

are living creatures devoid of sense and, for the most part, rooted to the ground.'

Now, this is really a very good answer, as far as it goes, and truly expresses the distinction existing between the immense majority of the two groups of living things. Nevertheless, here again the discovery of fresh phenomena has brought us face to face with difficulties and puzzles, some of which seem, as yet, insoluble.

To put as shortly as possible what appears to be the outcome of modern scientific progress, it has, on the one hand, served to render more marked the distinction between living beings and creatures devoid of life; while, on the other hand, it has continually made more and more evident that (in spite of the distinctions between most of them) animals and plants form one great whole, and inust be scientifically treated together, as well as separately.

Thus, to the two sciences of zoology and botany, which refer to animals and plants respectively, we have now added a fresh science, the science of BIOLOGY, which treats of animals and plants taken together, collectively, as forming one great group.

That the reader may have some faint notion how vast this great group is, it may be well hastily to survey the main classes of creatures which together compose it. We think it desirable to do so, because very inadequate images are apt to rise before the minds of most persons unacquainted with natural science, when they use such words as 'animals' and 'plants,' since they naturally think most of those with which they are the most familiar.

Thus, they are familiar with certain beasts, birds, reptiles, and fishes, but know little about the number of them. Of birds, ten thousand distinct kinds are known, and upwards of four thousand kinds of lizards, and sixteen hundred kinds of snakes have been described; while fishes are so rich in

species that they probably equal in the number of their kinds the whole mass of beasts, birds, and reptiles taken together!

But such creatures as these form but a very small proportion of all animals. Creatures such as snails and oysters form another vast group, known as 'mollusks.'

Worms, also, have been formed into a division, so varied in nature and so prodigious in number that their proper classification is amongst the most difficult of zoological problems.

The star-fishes and their allies constitute another great group, rich both in species and diversities of form.

But the whole of the creatures we have yet referred to, taken together in one mass, are far exceeded in the number of their distinct species by the class of insects alone (of which one or more are associated with the life of each and every land plant, and probably that of every higher animal also); while closely allied to insects are the multitudinous tribes of lobsters, shrimps, crabs, spiders, and scorpions.

We have also to take into account those coral animals which have actually built up large tracts of the earth's habitable surface; and besides these, we have their humble followers, the sponges.

All the creatures yet referred to are cognisable by our ordinary senses; but there are, as is commonly known, myriads of kinds, either so small as to be altogether invisible to the naked eye, or else invisible as regards the main points of their structure without the aid of the microscope. All the lowest animals, the bodies of which are not made up of distinct organic substances, or tissues, are called PROTOZOA.

Then, as to plants: besides the families of flowering trees, shrubs, creepers, and herbs, with members of which we unconsciously become more or less familiar, there are a multitude of other families, specimens of which we only see in our

occasional visits to the hot-houses of our botanical gardens. To these follow the almost numberless kinds of plants which do not flower-the ferns, horse-tails, grasses, lichens, seaweeds (with their fresh-water allies), and fungi. Parallel with the microscopic creatures ordinarily classed as 'animals' are the microscopic plants, some of which have been, till of late years, the despair of the surgeon; while others are now recognised as, or suspected to be, the cause and origin of the most painful and dangerous diseases.

Multitudinous, however, as is the animal and vegetable life which we have about us to-day, it is but a remnant of that of which this planet has been the theatre; and especially wonderful are the discoveries of fossil remains which have been made in North America, revealing to us the past existence of living forms such as had not been pictured even in the recorded musings of any naturalist. Apart from such wonderful scientific novelties, we have in the ancient chalk cliffs, and the far more ancient coal-fields, abundant evidence of the prodigality and duration of past vitality. The chalk is, as it were, still in process of formation, as the ooze slowly forming in the bed of the Atlantic Ocean. The coal affords evidence that rich vegetable life flourished at a period so remote that during it the first appearance of the chalk might have seemed as the dream of an infinitely distant future.

It is this immensely complex mass of living beings which we have to regard, in their totality, as one whole, as well as in their two component groups, if we would know what 'animals' and 'plants' really are.

But in order that we may learn what they are, it will be well first to advert briefly to one or two facts concerning things which are neither plants nor animals, certain facts, that is, about the inorganic world,' by which we mean the solid earth with its two envelopes-water and air. All the substances of which this inorganic world is composed are

either (1) elements, such e.g. as the gas oxygen or the metal iron; or (2) compounds of elements, such, e.g., as rust, which consists of oxygen and iron united to form a third substance which is neither the one nor the other.

Very many substances can exist (as water can) in three states, solid (ice), fluid (water), aëriform (vapour).

A solid inorganic substance may be either in the form of crystal (as marble) or not crystalline (as chalk), while having all the time the same chemical composition. Thus both marble and chalk can be resolved into (1) lime and (2) a gas, commonly known as carbonic acid gas, and carbonic acid is again resolvable into (1) oxygen and (2) carbon, or pure

charcoal.

The aëriform envelope of this planet—that is, AIR—is a mixture of the two gases (1) oxygen and (2) nitrogen, with some carbonic acid gas and a certain amount of ammonia and the vapour of water.

Oxygen, itself incombustible, is the great burner or aider of combustion.

Nitrogen is remarkable at once both for its own inertness and for its instability; so that it is an ingredient in all the most explosive compounds, such as gunpowder, guncotton, nitroglycerine and the iodide, sulphide, and chloride of nitrogen.

Of carbonic acid there are ordinarily but four cubic feet in ten thousand cubic feet of air; yet so great is the quantity of it contained in the whole atmosphere that there are reckoned to be 371,475 tons of it in the column of atmosphere which extends above each square mile of the earth's surface.

WATER, the earth's fluid envelope, consists of oxygen, hydrogen, carbonic acid, ammonia, carbonate of lime, flint (in solution), and sundry salts. It is, as it were, the mother substance of life, both historically and physiologically, and has been a great agent in both the production and the destruction