Before the invention of the microscope, no independent voluntary movements, if we except the opening and closure of flowers, and their turning towards the sun, the drooping of the leaves of sensitive plants under irritation, and some other kindred phenomena, were known in plants. Now, however, we know of many plants which are endowed, either when young or throughout life, with the power of effecting voluntary movements apparently as spontaneous and independent as those performed by the lower animals, the movements being brought about by means of little vibrating cilia, or hairs, with which a part or the whole of the surface is furnished. When it is added that many animals are permanently rooted, in their fully-grown condition, to solid objects, it will at once be apparent that no absolute distinction can be made between animals and plants merely because of the presence or absence of independent locomotive power.
There is, however, a test, the most reliable of all that have been discovered, by which an animal may be distinguished from a plant, and that is the nature of the food and the products which are elaborated therefrom in the body. Plants live upon such inorganic substances as water, carbonic acid and ammonia, and they have the power of manufacturing out of these true organic materials, and are therefore the great producers of nature. All plants which contain green coloring matter, technically called chlorophyll, break up carbonic acid in the process of digestion into its two constituents of carbon and oxygen, retaining the former and setting the latter free. And as the atmosphere always contains carbonic acid in small quantities, the result is that plants remove carbonic acid therefrom and give out oxygen. Animals, on the other hand, have no power of living on water, carbonic acid and ammonia, nor of converting these into the complex organic substances of their bodies. That their existence may be maintained animals require to be supplied with ready-made organic compounds, and for these they are all dependent upon plants, either directly or indirectly. In requiring as food complex organic bodies, which they ultimately reduce to very simply inorganic ones, animals are thus found to differ from plants. Whilst plants are the great manufacturers in nature, animals are the great consumers. Another distinction, arising from the nature of their food, is that animals absorb oxygen and throw out carbonic acid, their reaction upon the atmosphere being exactly the reverse of that of plants. There are organisms, it must be understood, which are genuine plants so far as their nutritive processes are concerned, but which, nevertheless, are in the possession of characters which could locate them among the animals. Volvox, so abundant in our streams during the proper seasons, affords a splendid illustration of the truth of this statement. Plants, which are devoid of chlorophyll, as is the case with the Fungi, do not possess the power of decomposing carbonic acid under the influence of sunlight, but are like animals in requiring organic compounds for their food. Two points must therefore be borne in mind in regarding the general distinctions between plants and animals which we have thus briefly outlined, and these are that they cannot often be applied in practice to ambiguous microscopic organisms, and certainly not to plant-forms that are destitute of chlorophyll.
That life should manifest itself certain conditions are essential, but some of which, though generally present, are not absolutely indispensable. One condition, however, seems to be very necessary, and that is that the living body should be composed of a certain material. This material, which forms the essential and fundamental parts of everything living, whether vegetable or animal, is technically called protoplasm. Other substances than it are often found in living bodies, but it is in protoplasm only that vitality appears to be inherent.
But whether it is the same in plants as in animals is a matter of opinion. One thing, however, seems reasonably certain, and that is that it is the medium or vehicle through which vital force is made manifest. Used in its general sense, protoplasm is chemically related in its nature to albumen, and generally has the character of a jelly-like, semi-fluid, transparent material, which, in itself, exhibits no definiteness of structure. When heated to a certain temperature it coagulates, just as the white of an egg does when boiled. Living protoplasm has the power of movement, of increasing in size or of maintaining its existence by the assimilation of fresh and foreign materials, and of detaching portions of itself which may subsequently develop into fresh masses. Though protoplasm be present in the ova of animals and the seeds of plants, yet there is no external and visible manifestation of life. There is in them what is called a dormant vitality, which may remain for a long time unchanged, until altered external circumstances cause the organism to pass into a state of active life.
Generally, certain external conditions must be present before any external vital phenomena can be manifested. The presence of atmospheric air, or rather of free oxygen, is in an ordinary way essential to active life. Life, that is its higher manifestations, is only possible between certain ranges of temperature, varying from near the freezing point to about 120° Fahrenheit. As water is a necessary constituent of protoplasm in its living state, so it becomes an absolutely essential requisite to the carrying on of vital processes of all kinds, for the mere drying of an animal or plant will, in most cases, kill it outright, and will always bring about a suspension of all visible life-phenomena.
While the large majority of living beings are organized, or composed of different parts, called organs, which sustain certain relations with one another, and which discharge different offices, yet it must not therefore be concluded that organization is a necessary accompaniment of vitality, or that all living creatures are organized. Innumerous low forms of life, so low that they occupy the very lowest place in the scale of animated existences, absolutely exhibit no visible structure, and cannot, therefore, be said to be organized, but they, nevertheless, discharge all their vital functions just as well as though they possessed special organs for the purpose. Concluding our theme, we are forced to admit that animals are organized, or possess structure, because they are alive, and not that they live because they are organized. By carefully comparing the morphological and physiological differences between different animals and plants, naturalists have divided the entire animal and vegetable kingdoms into a number of divisions, whose leading characteristics may be found in almost every text-book. All that we promised ourselves when this work was first thought of was a brief treatment of a few of the most interesting life-forms of this planet of ours in the light of their ways and doings, and the direction of human thought to those traits of character and manifestations of conscious intelligence which fit them to become partakers with man of that new life which awaits him beyond the grave.
PLANTS THAT FEED ON INSECTS.
Perhaps it would be difficult to find in the whole range of vegetable creation anything more curious than the carnivorous or flesh-eating plants. That animals eat plants creates in us no emotion of curiosity, for this is the common law of nature. But that plants should devour animals is a marvel to which few minds uninitiated in science would give credence. Though these strange forms of vegetable life have been known for about a century, yet it has been but a few years since the attention of naturalists was first specially called to their habits and character. No one has probably done more to explain the life and operations of the flesh-eating plants than Mr. Darwin.
For centuries strange rumors had been circulated of the existence of huge plants in the more remote and unvisited parts of Asia which would imprison and destroy large animals and men that would venture within reach of their great quivering leaves armed with hooked spines, the flesh of the dead victim being absorbed into their structure, but all these giant flesh-eating trees or plants have so far proved to be mere myths. Science has discovered, however, that there is some foundation for these exciting fictions, and it has not been obliged to go to the distant East to find it, for flesh-eating plants are by no means uncommon in this country and Europe. But these plants confine their destructive propensities to the crawling and flying insects which are beguiled by some tempting reward to rest on their leaves. Such a strange provision of nature is no less interesting than if these plants had the power to destroy the larger animals, for it is the fact itself which startles the attention by its seeming reversal of natural laws.
No better example of carnivorous plants could be taken than Dionæa muscipula, or to use the common name, Venus’s Fly-trap. It is a species that is indigenous to North Carolina and the adjacent parts of South Carolina, affecting sandy bogs in the pine forests from April to June, and a representative of the Droscraceæ, or Sundew Family. One cannot fail after once seeing it of becoming impressed with its peculiar characteristics. It is a smooth perennial herb with tufted radical leaves on broadly-winged, spatulate stems, the limb orbicular, notched at both ends, and fringed on the margins with strong bristles. From the centre of the rosette of leaves proceeds at the proper time a scape or leafless stalk which terminates in an umbel-like cyme of from eight to ten white bracted flowers, each flower being one inch in diameter. The roots are small and consist of two branches each an inch in length springing from a bulbous enlargement. Like an epiphytic orchid, these plants can be grown in well-drained damp moss without any soil, thus showing that the roots probably serve for the absorption of water solely. Three minute pointed processes or filaments, placed triangularly, project from the upper surface of each lobe of the bi-lobed leaf, although cases are observed where four and even ten filaments are found. These filaments are remarkable for their extreme sensitiveness to touch, as shown not only by their own movement, but by that of the lobes also. Sharp, rigid projections, diminutive spikes as it were, stand out from the leaf-margins, each of which being entered by a bundle of spiral vessels. They are so arranged that when the lobes close they interlock like the teeth of an old-fashioned rat-trap. That considerable strength may be had, the mid-rib of the leaf, on the lower side, is quite largely developed.