dog may howl painfully at our sweet music. We call the apple-blossom and the butterfly's wings beautiful, partly because the rays of light, borne from them to our eyes, cause a pleasantly harmonious activity in our brains, partly because this awakens reminiscences of past pleasant experiences, partly for subtler reasons. Still, all healthy organisms are harmonious in form, and seldom if ever are their colours out of tone with their surroundings or with each other,—a fact which suggests the truth of the Platonic conception that a living creature is harmonious because it is possessed by a single soul, the realisation of a single idea.

The plants which seem to many eyes to have least beauty are those which have been deformed or discoloured by cultivation, or taken altogether out of their natural setting; the only ugly animals are the products of domestication and human interference on the one hand, or of disease on the other; and the ugliest things are what may be called the excretions of civilisation, which are certainly not beauty for ashes, but productions by which the hues and colours of nature have been destroyed or smothered, where the natural harmony has been forcibly put out of tune-in short, where a vicious taste has insisted on becoming inventive.

CHAPTER II

THE WEB OF LIFE

1. Dependence upon Surroundings-2. Inter-relations of Plants and Animals-3. Relation of Animals to the Earth-4. Nutritive Relations-5. More Complex Interactions

IN the filmy web of the spider, threads delicate but firm bind part to part, so that the whole system is made one. The quivering fly entangled in a corner betrays itself throughout the web; often it is felt rather than seen by the lurking spinner. So in the substantial fabric of the world part is bound to part. In wind and weather, or in the business of our life, we are daily made aware of results whose first conditions are remote, and chains of influence not difficult to demonstrate link man to beast, and flower to insect. The more we know of our surroundings, the more we realise the fact that nature is a vast system of linkages, that isolation is impossible.

1. Dependence upon Surroundings.—Every living body is built up of various arrangements of at least twelve “elements,” viz. Oxygen, Hydrogen, Carbon, Nitrogen, Chlorine, Phosphorus, Sulphur, Magnesium, Calcium, Potassium, Sodium, and Iron. All these elements are spread throughout the whole world. By the magic touch of life they are built up into substances of great complexity and instability, substances very sensitive to impulses from, or changes in, their surroundings. It may be that living matter differs from dead matter in no other way than this. The

varied forms of life crystallise out of their amorphous beginnings in a manner that we conceive to be analogous to the growth of a crystal within its solution. Further, we do not believe in a "vital force." The movements of living things are, like the movements of all matter, the expression of the world's energy, and illustrate the same laws. But to these matters we shall return in another chapter.

Interesting, because of its sharply defined and far-reaching significance, and because the essential mass is so nearly infinitesimal, is the part played by iron in the story of life. For food-supply we are dependent upon animals and plants, and ultimately upon plants. But these cannot produce their valuable food-stuffs without the green colouring-matter in their leaves, by help of which they are able to utilise the energy of sunshine and the carbonic acid gas of the air. But this important green pigment (though itself perhaps free from any iron) cannot be formed in the plant unless there be, as there almost always is, some iron in the soil. Thus our whole life is based on iron. And all our supplies of energy, our powers of doing work either with our own hands and brains, or by the use of animals, or through the application of steam, are traceable—if we follow them far enough—to the sun, which is thus the source of the energy in all creatures.

2. Inter-relations of Plants and Animals. We often hear of the "balance of nature," a phrase of wide application, but very generally used to describe the mutual dependence of plants and animals. Every one will allow that most animals are more active than most plants, that the life of the former is on an average more intense and rapid than that of the latter. For all typical plants the materials and conditions of nutrition are found in water and salts absorbed by the roots, in carbonic acid gas absorbed by the leaves from the air, and in the energy of the sunlight which shines on the living matter through a screen of green pigment. Plants feed on very simple substances, at a low chemical level, and their most characteristic transformation of energy is that by which the kinetic energy of the sunlight is changed into the potential

energy of the complex stuffs which animals eat or which we use as fuel. But animals feed on plants or on creatures like themselves, and are thus saved the expense of building up food-stuffs from crude materials. Their most characteristic transformation of energy is that by which the power of complex chemical substances is used in locomotion and work. In so working, and eventually in dying, they form waste-products-water and carbonic acid, ammonia and nitrates, and so on—which may be again utilised by plants.

How often is the inaccurate statement repeated "that animals take in oxygen and give out carbonic acid, whereas plants take in carbonic acid and give out oxygen"! This is most misleading. It contrasts two entirely distinct processesa breathing process in the animal with a feeding process in the plant. The edge is at once taken off the contrast when the student realises that plants and animals being both (though not equally) alive, must alike breathe. As they live the living matter of both is oxidised, like the fat of a burning candle; in plant, in animal, in candle, oxygen passes in, as a condition of life or combustion, and carbonic acid gas passes out as a waste-product. Herein there is no difference except in degree between plant and animal. Each lives, and must therefore breathe. But the living of plants is less intense, therefore the breathing process is less marked. Moreover, in sunlight the respiration is disguised by an exactly reverse process peculiar to plants—the feeding already noticed, by which carbonic acid gas is absorbed, its carbon retained, and part of its oxygen liberated.

There is an old-fashioned experiment which illustrates the "balance of nature." In a glass globe, half-filled with water, are placed some minute water-plants and wateranimals. The vessel is then sealed. As both the plants and the animals are absorbing oxygen and liberating carbonic acid gas, it seems as if the little living world enclosed in the globe would soon end in death. But, as we have seen, the plants are able in sunlight to absorb carbonic acid and liberate oxygen, and if present in sufficient numbers will

compensate both for their own breathing and for that of animals. Thus the result within the globe need not be suffocation, but harmonious prosperity. If the minute animals ate up all the plants, they would themselves die for lack of oxygen before they had eaten up one another, while if the plants smothered all the animals they would also in turn die away. Some such contingency is apt to spoil the experiment, the end of which may be a vessel of putrid water tenanted for a long time by the very simple colourless plants known as Bacteria, and at last not even by them. Nevertheless the "vivarium" experiment is both theoretically and practically possible. Now in nature there is, indeed, no closed vivarium, for there is no isolation and there is open air, and it is an exaggeration to talk as if our life were dependent on there being a proportionate number of plants and animals in the neighbourhood. Yet the "balance of nature" is a general fact of much importance, though the economical relations of part to part over a wide area are neither rigid nor precise.

We have just mentioned the very simple plants called Bacteria. Like moulds or fungi, they depend upon other organisms for their food, being without the green colouring stuff so important in the life of most plants. These very minute Bacteria are almost omnipresent; in weakly animals -and sometimes in strong ones too--they thrive and multiply and cause death. They are our deadliest foes, but we should get rid of them more easily if we had greater love of sunlight, for this is their most potent, as well as most economical antagonist. But it is not to point out the obvious fact that a Bacterium may kill a king that we have here spoken of this class of plants; it is to acknowledge their beneficence. They are the great cleansers of the world. Animals die, and Bacteria convert their corpses into simple substances, restoring to the soil what the plants, on which the animals fed, originally absorbed through their roots. Bacteria thus complete a wide circle; they unite dead animal and living plant. For though many a plant thrives quite independently of animals on the raw materials of earth and air, others are demonstrably raising