Fertilization of the flowers is provided for in a similar manner. The flowers can not reach each other, and therefore enlist insects in their aid, preparing a store of food highly palatable to these air rovers, and thus having their fertilizing germs carried from flower to flower.
Such are the general agencies at work in plant-life, and producing its typical form. And thus, while protecting their vital organs by a rigid armor, plants provide for reproduction by adapting a portion of their bodies for animal food; gaining in this manner for their offspring the powers of motion which they lack themselves.
Yet all plants are not confined to this typical form, as all plants are not confined to purely inorganic aliment. Some subsist on partly or fully elaborated organic food, and these deviate from the plant and approach some of the animal types of form, which we have next to consider.
In animal life very different requirements from those presented by plants are exhibited, and the forms are essentially different. Yet their main functions are the same. All organisms are adapted to the two general purposes of food-getting and defense, to which all their other powers are subordinate.
As vegetables subsist on mineral, so animals subsist on organic food, either vegetable or animal. And this food presents another essential difference from that of plants. It exists only in the solid state, while that of plants is wholly fluid. It can not be taken by direct imbibition, like that of vegetables, but must be first rendered liquid through some digestive process, and afterward imbibed. Thus an internal stomach is necessary to all but the very lowest animals, and even these improvise temporary stomachs, which foreshadow the permanent stomach.
The animal—not being bathed in an ocean of food, which it has but to drink in at a multitude of mouths covering its whole periphery, as in the plant—must have means of drawing food to it, or organs enabling it to go in search of food. In short, it must have motive powers.
And for those creatures which are obliged to go in search of their food, it is equally requisite that they should be able to discover its locality. Sensory organs, therefore, become necessary. Consequently, the animal is superior to the plant through this possession of muscular and sense organs. It is also superior in being able to employ the energy derived from its food, not in the building up of chemical compounds, but in the force of motion and sensation.
Nor can the animal be wholly protected by armor. Some portion of it must be exposed to danger. At least those flexible limbs which aid it in food-getting are in frequent peril, and need some form of protection. The loss of them can not well be made useful to the animal, as the loss of its exposed portions is to the plants.
Evidently the animal is capable of a much wider range of form evolution than the plant. In its mobility of variation it has branched
